Free Unit Converter Online
The all-in-one online unit converter for every measurement — length, weight, temperature, area, volume, pressure, torque, energy, power, speed, time, density, flow rate, viscosity, and electric capacitance. 200+ units, instant conversion, no signup.
All-in-One Unit Converter — Every Measurement Category in One Tool
From everyday length and weight conversions to advanced physics units like torque, viscosity, and flow rate — every category is covered with accurate, NIST-aligned conversion factors.
Length
nm, mm, cm, m, km, inch, foot, yard, mile, nautical mile. Covers mm to feet and meter conversions.
Weight / Mass
μg, mg, g, kg, metric ton, oz, lb, stone, short ton, long ton. Includes mg to g and kg to lb.
Temperature
Celsius, Fahrenheit, Kelvin, Rankine. Non-linear formulas handled automatically.
Volume
mL, L, m³, fl oz, cup, pint, quart, US gallon, UK gallon, tsp, tbsp, in³, ft³ and more.
Area
mm², cm², m², km², in², ft², yd², acre, hectare, mi². Perfect as a land area unit converter.
Speed
m/s, km/h, mph, knots, ft/s, Mach, and speed of light. For physics and everyday travel speed.
Time
Nanoseconds to years — ns, μs, ms, seconds, minutes, hours, days, weeks, months, years.
Pressure
Pa, hPa, kPa, MPa, bar, mbar, PSI, atm, mmHg, inHg. Includes tire/tyre pressure conversion.
Energy
J, kJ, MJ, GJ, cal, kcal, Wh, kWh, MWh, BTU, ft·lb. Watt-to-unit converter included.
Power
W, kW, MW, GW, HP (mechanical & metric), BTU/hr, kcal/hr. kW to HP and watt conversions.
Torque
N·m, kN·m, N·cm, lb·ft, lb·in, kgf·m, kgf·cm, ozf·in. The torque unit converter calculator for engineering.
Density
kg/m³, g/cm³, g/mL, kg/L, lb/ft³, lb/in³, lb/gal. Used in science, engineering, and materials.
Flow Rate
m³/s, m³/h, L/s, L/min, mL/s, gal/min, gal/hr, ft³/s, ft³/min and more volumetric flow units.
Viscosity
Pa·s, mPa·s, cP (centipoise), poise, dPa·s, μPa·s, kPa·s. Dynamic viscosity for fluids and materials.
Electric (Capacitance)
kF, F, mF, μF, nF, pF. The farad unit converter for electronics, capacitors, and electrical engineering.
Convert Any Unit in 3 Simple Steps
This free online unit converter is designed to be fast and frictionless. No forms to fill, no account needed — just pick, type, and read your answer.
Choose a Category
Click any of the 15 category tabs at the top of the converter — Length, Weight, Temperature, Pressure, Energy, or any other measurement type. The converter instantly loads the correct unit options for that category.
Select Units & Enter Value
Pick your From unit and To unit from the dropdowns. Type your value in the input field. The conversion happens instantly as you type — no button to press. Hit the ⇄ swap button to reverse the direction at any time.
Read the Result
See your converted value in the blue result box instantly. The formula bar below explains the exact calculation. The Quick Reference panel shows conversions to several other units at once. Use the Copy button to copy the result to your clipboard.
Why Use WebToolTrix Unit Converter?
Built to be faster, cleaner, and more useful than a basic search result — with categories most free tools skip entirely.
All Unit Categories in One Place
Most tools only cover 5–7 categories. This converter covers 15 — including advanced science units like torque, viscosity, flow rate, density, and electric capacitance that most free tools skip.
Instant, Real-Time Conversion
Results appear as you type. No submit button, no page reload. The formula bar updates live so you always see exactly how the conversion was calculated.
Quick Reference Table
Below every conversion you get a Quick Reference panel showing your input value converted to 6–8 other common units at once — functioning like an interactive unit converter chart.
100% Private & Browser-Based
All calculations run entirely in your browser. Nothing is sent to any server. No cookies, no tracking, no account required. Your data never leaves your device.
Mobile-Friendly Design
The full-width layout adapts cleanly to any screen size. Category tabs scroll horizontally on mobile so all 15 categories are always one tap away.
NIST-Aligned Conversion Factors
Every conversion factor is sourced from NIST (National Institute of Standards and Technology) and SI standards to ensure accuracy in science, engineering, education, and everyday use.
Metric vs. Imperial Unit Converter Chart
A quick-reference unit converter table comparing the most common measurement systems — metric (SI), US customary, and imperial — across everyday unit categories.
| Category | Metric (SI) | US Customary | Imperial (UK) | Key Conversion |
|---|---|---|---|---|
| Length | meter, kilometer, centimeter | inch, foot, yard, mile | inch, foot, yard, mile | 1 m = 3.28084 ft |
| Weight / Mass | kilogram, gram, tonne | pound, ounce, short ton | pound, stone, long ton | 1 kg = 2.20462 lb |
| Volume | liter, milliliter, m³ | US gallon, US fl oz, cup | UK gallon, UK fl oz | 1 L = 0.26417 US gal |
| Temperature | Celsius (°C), Kelvin (K) | Fahrenheit (°F) | Fahrenheit (°F) | °F = (°C × 9/5) + 32 |
| Area | m², hectare, km² | ft², acre, mi² | ft², acre, mi² | 1 ha = 2.47105 acres |
| Pressure | Pascal, kPa, bar | PSI, inHg | PSI, bar | 1 psi = 6.89476 kPa |
| Speed | m/s, km/h | mph, ft/s | mph, knots | 1 km/h = 0.62137 mph |
| Energy | Joule, kWh, calorie | BTU, ft·lb | BTU, ft·lb | 1 kWh = 3412.14 BTU |
| Power | Watt, kilowatt | HP (mechanical) | HP (metric / PS) | 1 kW = 1.34102 HP |
| Torque | Newton·meter (N·m) | pound-foot (lb·ft) | pound-foot (lb·ft) | 1 N·m = 0.73756 lb·ft |
The Complete Guide to Unit Conversion: All Measurement Categories Explained
Whether you are a student working through physics homework, an engineer reading international specifications, a cook scaling a recipe, or a traveler figuring out how fast you are driving in a foreign country, you will run into the need to convert between units of measurement. A reliable free unit converter online eliminates the guesswork and manual arithmetic — giving you instant, accurate results for any measurement type.
This guide walks through every major unit category covered by this tool, explaining what each unit measures, which conversion formulas matter most, and when you are likely to need them in everyday life, academic work, or professional settings.
Length Unit Converter
Length (or distance) is one of the most frequently converted measurement types. The metric system uses the meter as its base unit, with prefixes scaling it by powers of ten (millimeter, centimeter, kilometer). The US customary and imperial systems use inches, feet, yards, and miles — a less intuitive hierarchy that makes conversions especially prone to errors without a tool.
Length Unit Converter Table — Common Conversions
| From | To | Factor |
|---|---|---|
| 1 Meter (m) | Feet (ft) | × 3.28084 |
| 1 Kilometer (km) | Miles (mi) | × 0.62137 |
| 1 Inch (in) | Centimeters (cm) | × 2.54 |
| 1 Foot (ft) | Meters (m) | × 0.3048 |
| 1 Mile (mi) | Kilometers (km) | × 1.60934 |
| 1 Yard (yd) | Meters (m) | × 0.9144 |
How to Convert mm to Feet
One of the most searched length conversions is millimeters to feet — common in construction drawings, product specs, and woodworking. Since 1 foot = 304.8 mm, the formula is simple: feet = mm ÷ 304.8. For example, 1500 mm = 4.921 feet. Going the other way: mm = feet × 304.8. Use the Length tab in the converter above and select Millimeter → Foot for instant mm-to-feet results.
The meter unit converter is equally essential for international work. The US remains one of the few countries not officially using the metric system, so meter-to-foot and kilometer-to-mile conversions come up constantly in international trade, sports, and travel.
Weight and Mass Unit Converter
Weight and mass are technically different physical quantities, but in everyday usage the terms are interchangeable. The SI unit for mass is the kilogram (kg). The US customary system uses pounds (lb) and ounces (oz). Scientific contexts use smaller metric units like milligrams (mg) and micrograms (μg).
Converting mg to g and Other Weight Units
The mg to g conversion is a staple in pharmacy, nutrition labels, and laboratory science. The rule is simple: 1 gram = 1,000 milligrams, so divide mg by 1,000 to get grams. Common examples: a standard aspirin tablet is 325 mg (0.325 g); the recommended daily vitamin D intake is 600–800 IU, which for cholecalciferol corresponds to about 15–20 μg.
For everyday use, the most important unit converter weight relationship is kilograms to pounds: 1 kg = 2.20462 lb. Body weight in the US is measured in pounds; elsewhere in kg. A 150 lb person weighs about 68 kg. A 70 kg person weighs about 154.3 lb.
Temperature Unit Converter
Temperature is unique among units because conversions are not multiplicative — they involve an offset as well. The three scales in common use are Celsius (°C), used globally and in science; Fahrenheit (°F), used in the US for weather and cooking; and Kelvin (K), the SI unit for thermodynamics.
The key formulas: °F = (°C × 9/5) + 32 and K = °C + 273.15. Water freezes at 0°C / 32°F / 273.15 K and boils at 100°C / 212°F / 373.15 K. Body temperature is 37°C / 98.6°F. The temperature tab above handles all four scales (including Rankine, used in some US engineering applications) automatically.
Area Unit Converter — Including Land Area
Area measurement uses squared length units. The metric system's base area unit is the square meter (m²), with the hectare (ha) — equal to 10,000 m² — as the standard for land measurement in most of the world. In the US, land is measured in acres: 1 acre = 4,046.86 m² = 0.404686 ha.
Land Area Unit Converter — Key Conversions
| From | To | Result |
|---|---|---|
| 1 Acre (ac) | Hectares (ha) | 0.404686 ha |
| 1 Hectare (ha) | Acres (ac) | 2.47105 acres |
| 1 Square mile (mi²) | Acres (ac) | 640 acres |
| 1 Square mile (mi²) | km² | 2.58999 km² |
| 1 Sq foot (ft²) | Sq meters (m²) | 0.092903 m² |
The land unit converter is essential for real estate transactions, agricultural planning, and comparing property sizes across international listings. A half-acre residential lot in the US equals roughly 0.2 hectares — a comparison that's helpful when browsing international property listings.
Volume Unit Converter
Volume conversion is particularly important in cooking, chemistry, and fluid mechanics. The US uses its own customary volume system (US cups, pints, quarts, gallons) that differs from the British imperial system — a source of much confusion. The metric system uses liters and milliliters.
Key facts for the volume unit converter calculator: 1 US gallon = 3.78541 liters (vs. 4.54609 liters for a UK gallon). 1 US cup = 236.588 mL. 1 fluid ounce (US) = 29.5735 mL. For cooking, the teaspoon (5 mL) and tablespoon (15 mL) are indispensable. Use the Volume tab to run any of these conversions instantly.
Pressure Unit Converter
Pressure measures force per unit area. The SI unit is the Pascal (Pa), but practical applications use a range of other units depending on context. The pressure unit converter calculator supports ten units including PSI, bar, kPa, atm, and mmHg.
Tire Pressure and Air Pressure Unit Converter
The most common everyday pressure conversion is tire (tyre) pressure. In the US, tire pressure is measured in PSI (pounds per square inch). In Europe and Australia, it's typically bar or kPa. A car tire inflated to 32 PSI = 2.21 bar = 220.6 kPa.
The air pressure unit converter is also critical in meteorology. Standard atmospheric pressure is 101,325 Pa = 1 atm = 1013.25 hPa (millibar). Weather apps typically show pressure in hPa or mbar. Mercury barometers use mmHg or inHg — 760 mmHg = 1 atm.
Energy, Power, and Torque Unit Converters
Energy Unit Converter (kWh, BTU, Joules)
The unit converter energy category covers the full range from tiny joules to massive gigajoules. For electricity consumption, the kilowatt-hour (kWh) is the billing unit — 1 kWh = 3,412 BTU = 3.6 MJ. For food energy, calories (kcal) are used — 1 kcal = 4,184 joules. BTUs (British Thermal Units) measure heat capacity in HVAC systems and gas appliances.
The kWh to unit converter and watt to unit converter are frequently needed by engineers, energy auditors, and homeowners comparing appliance energy consumption. For instance, a 1,500W space heater running for 2 hours uses 3 kWh = 10,236 BTU = 10.8 MJ.
Power Unit Converter (kW to HP)
Power measures how quickly energy is used. The unit converter power category supports watts, kilowatts, megawatts, and horsepower. The kW to unit converter is especially important in the automotive and industrial sectors: 1 kW = 1.34102 mechanical HP (or 1.35962 metric HP / PS). A 200 HP engine produces approximately 149 kW.
Torque Unit Converter Calculator
Torque is the rotational equivalent of force — it measures how much twisting force is applied to an object. The SI unit is the Newton-meter (N·m); in the US, engine torque is specified in pound-feet (lb·ft). The torque unit converter calculator is essential for automotive mechanics, machine design, and fastener tightening specifications: 1 N·m = 0.7376 lb·ft; 1 lb·ft = 1.35582 N·m.
Speed, Time, and Density Unit Converters
The unit converter for speed handles m/s, km/h, mph, knots, and Mach. The most common conversion: 1 km/h = 0.62137 mph. Speed limits in Europe are in km/h; in the US in mph. A 100 km/h speed limit equals 62.1 mph. The Mach number is contextual — Mach 1 at sea level equals ~340.3 m/s or 767 mph.
The time unit converter covers nanoseconds through years. This is useful for computing (CPU clock cycles in nanoseconds), project management (days to weeks), and physics (half-lives in seconds). One year (Julian) = 365.25 days = 8,766 hours = 31,557,600 seconds.
The unit converter density supports kg/m³, g/cm³, g/mL, and imperial equivalents. Water's density is exactly 1 g/cm³ = 1 kg/L = 1000 kg/m³ — a useful reference point. Lead is about 11.3 g/cm³; aluminum is 2.7 g/cm³.
Advanced Unit Converters: Flow Rate, Viscosity, and Electric Capacitance
Flow Rate Unit Converter
The flow rate unit converter measures volumetric flow — how much fluid moves through a system per unit time. Units include m³/s, L/min, and gallons per minute (GPM). This is critical for pump selection, HVAC engineering, plumbing, and chemical processing. A standard garden hose flows approximately 9–17 liters per minute (2.4–4.5 GPM).
Viscosity Unit Converter
Dynamic viscosity measures a fluid's resistance to flow. The SI unit is Pascal-second (Pa·s), but the centipoise (cP) is widely used in industry. Water at 20°C has a viscosity of approximately 1 cP = 1 mPa·s. Motor oil is typically 100–200 cP. The viscosity unit converter supports Pa·s, mPa·s, cP, poise, and more.
Farad Unit Converter — Electric Capacitance
The farad (F) is the SI unit of capacitance. One farad is very large — typical electronic capacitors range from picofarads (pF) to microfarads (μF). The farad unit converter supports kF, F, mF, μF, nF, and pF. Use it when reading component datasheets or designing electronic circuits. 1 μF = 1,000 nF = 1,000,000 pF.
Unit Conversion Formulas: A Reference for Science and Physics
For students and professionals using this as a unit converter for physics or a science unit converter, understanding the underlying formulas is essential. The universal formula for linear conversions is:
Result = Input × (Factorfrom ÷ Factorto)
Where each factor represents that unit's value in the base unit. This works for length (base: meter), mass (base: kilogram), time (base: second), and all other SI-based categories. Temperature is the only exception, requiring an additive offset formula.
The formula unit converter approach is especially important in dimensional analysis — a core skill in physics and chemistry where tracking units prevents errors in multi-step calculations.
Imperial Unit Converter and the US Customary System
The imperial unit converter (also called the US customary converter) remains essential because the United States continues to use non-metric units in everyday life — pounds, miles, Fahrenheit, gallons, and inches. Understanding when the US system differs from the British imperial system is important: a US gallon (3.785 L) is smaller than a UK gallon (4.546 L), and a US ton (short ton, 2,000 lb) differs from a UK ton (long ton, 2,240 lb). This tool handles all these distinctions correctly.
As global supply chains and scientific publishing push toward metric standardization, the ability to quickly convert between systems is increasingly valuable — whether you are reading a European engineering specification in the US, importing goods with metric dimensions, or comparing nutrition facts across country-specific packaging.
Unit Converter — Frequently Asked Questions
Answers to the most common questions about unit conversion formulas, specific conversions, and how to use this tool.
For most units, the unit conversion formula is: Result = Input × (From Factor ÷ To Factor). Every unit has a factor relative to a base unit (e.g., meters for length). Multiply the input value by the from-unit's factor, then divide by the to-unit's factor.
Example: 5 kilometers to miles. Kilometer factor = 1000 m. Mile factor = 1609.344 m. Result = 5 × (1000 ÷ 1609.344) = 3.107 miles.
Temperature is a special case because its scales are offset (not just multiplied). The formula for Celsius to Fahrenheit is: °F = (°C × 9/5) + 32.
To convert millimeters (mm) to feet (ft): divide by 304.8.
Formula: feet = mm ÷ 304.8
Examples: 100 mm = 0.3281 ft | 500 mm = 1.6404 ft | 1000 mm = 3.2808 ft
To go the other way (feet to mm): multiply by 304.8. Use the Length tab above — select Millimeter and Foot, then type your value.
To convert milligrams (mg) to grams (g): divide by 1,000.
Formula: grams = milligrams ÷ 1000
Examples: 500 mg = 0.5 g | 1000 mg = 1 g | 250 mg = 0.25 g
To convert grams to milligrams: multiply by 1,000. Select the Weight tab, choose Milligram (mg) and Gram (g), and enter your value.
Tire (tyre) pressure is most commonly measured in PSI (US), bar (Europe), or kPa (metric). Common conversion formulas:
- PSI to bar: divide by 14.5038 (e.g., 32 PSI = 2.21 bar)
- PSI to kPa: multiply by 6.89476 (e.g., 32 PSI = 220.6 kPa)
- bar to PSI: multiply by 14.5038 (e.g., 2.2 bar = 31.9 PSI)
Typical car tire pressure is 30–35 PSI (2.07–2.41 bar / 207–241 kPa). Use the Pressure tab above for any tyre pressure unit converter conversion.
Kilowatt-hour (kWh) is the standard unit for electrical energy billing. Key energy conversions:
- 1 kWh = 3,412.14 BTU
- 1 kWh = 3,600,000 joules (3.6 MJ)
- 1 kWh = 860 kilocalories (kcal)
- 1 BTU = 1,055.06 joules
Use the Energy tab to convert kWh, BTU, joules, calories, and more. The kWh to unit converter is one of the most common energy conversions in US households and commercial settings.
A torque unit converter converts between units of rotational force. Torque is commonly used in automotive engineering (engine torque specs), industrial machinery, and physics.
This tool supports: N·m, kN·m, N·cm, lb·ft, lb·in, kgf·m, kgf·cm, ozf·in.
Key conversions: 1 N·m = 0.7376 lb·ft | 1 lb·ft = 1.35582 N·m | 1 kgf·m = 9.80665 N·m
Use the Torque tab above to use the torque unit converter calculator.
The farad (F) is the SI unit of electrical capacitance — it measures how much electric charge a capacitor stores per volt. In practice, most capacitors are much smaller than 1 farad.
Common capacitance units and their relationships:
- 1 F = 1,000 mF (millifarads)
- 1 F = 1,000,000 μF (microfarads)
- 1 μF = 1,000 nF (nanofarads)
- 1 nF = 1,000 pF (picofarads)
Ceramic and film capacitors are typically in nF or pF. Electrolytic capacitors are in μF. Supercapacitors can reach farads. Use the Electric tab above as your farad unit converter.
For land area conversions, click the Area tab. This converter supports acres, hectares, square meters, square feet, square miles, and square kilometers — the key units for land measurement.
Common land area conversions:
- 1 acre = 0.404686 hectares
- 1 hectare = 2.47105 acres
- 1 acre = 43,560 ft²
- 1 km² = 100 hectares = 247.105 acres
The US typically uses acres for land; most other countries use hectares. This land unit converter handles both systems and is useful for real estate, agriculture, and construction.
This tool does not generate a downloadable unit converter chart PDF directly, but the Quick Reference panel below the converter functions as a live unit converter table — showing your input converted to multiple units simultaneously.
For a printable unit converter sheet, you can print the page from your browser (Ctrl+P / Cmd+P) and the Quick Reference table will be included. The comparison table on this page also serves as a ready-to-print unit converter chart covering the most common measurement systems.
The Google unit converter (built into search results) handles everyday categories like length, weight, and temperature well. However, it does not support advanced categories like torque, viscosity, flow rate, density, or electrical capacitance.
WebToolTrix offers several advantages: 15 categories vs. Google's ~8; a Quick Reference panel that converts to multiple units at once; a formula display so you understand the math; and full privacy since everything runs in your browser with no data sent to external servers.
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