Unit Converter
Convert between common units with formulas.
Result
About This Unit Converter
A unit converter translates a quantity from one measurement unit to another using standard conversion factors or formulas. This free unit converter covers eight everyday categories — length, weight, temperature, area, volume, speed, pressure, and energy — and shows the factor and reverse conversion with every result.
How to Use
Select a category, enter a value, choose the From and To units, then click Convert. Results show six decimal places plus the factor or formula and the reverse relation. Swap Units exchanges the selections instantly.
How Conversion Factors Work
Most conversions are simple ratios built on a base unit: meters for length, kilograms for weight, liters for volume. Each unit's factor states how many base units it contains; the converter routes through it:
result = value × (base units per "from" unit) ÷ (base units per "to" unit)
- value — the number you enter.
- base units per "from" unit — e.g. 1 mile = 1,609.344 meters.
- base units per "to" unit — e.g. 1 kilometer = 1,000 meters.
- result — the quantity in the target unit.
Worked example: 5 miles to kilometers — 5 × 1,609.344 ÷ 1,000 = 8.04672 km (about 8.05 km). Temperature is the exception, covered below.
Length Conversions
The imperial–metric bridge rests on exact definitions: 1 in = 2.54 cm exactly (international agreement, 1959), which makes 1 ft = 0.3048 m and 1 mi = 1.609344 km exact too. Other handy pairs: 1 m = 3.28084 ft, 1 km = 0.621371 mi, 1 yd = 0.9144 m — so a 5K race is 5 × 0.621371 = 3.10686 miles.
Weight Conversions
Weight factors are built on the kilogram: 1 kg = 2.20462 lb, 1 lb = 0.453592 kg, 1 oz = 28.3495 g, 1 stone = 14 lb. Worked example: 70 kg to pounds — 70 × 2.20462 = 154.32 lb (154.3 lb rounded to one decimal). Converting body weight for a health check? Plug it into our BMI Calculator.
Temperature Conversions: Formulas, Not Factors
Temperature scales start at different zero points — 0 °C is already 32 °F — so multiplication alone fails. Use these formulas:
°F = °C × 9/5 + 32°C = (°F − 32) × 5/9K = °C + 273.15
Worked examples: 100 °C = 100 × 9/5 + 32 = 212 °F (boiling water); 37 °C = 98.6 °F (body temperature); −40 °C = −40 °F, where the scales meet. Kelvin just shifts Celsius: 0 °C = 273.15 K, so 300 K = 26.85 °C. A temperature difference converts without the offset: a 10 °C rise is an 18 °F rise.
Volume Conversions
This converter uses US customary volume units: 1 US gal = 3.78541 L, 1 L = 0.264172 gal, 1 qt = 0.946353 L, 1 cup = 236.588 mL, 1 fl oz = 29.5735 mL. Worked example: a 5-gallon gas can holds 5 × 3.78541 = 18.92705 L, about 18.93 L. Don't confuse this with the UK's imperial gallon — at 4.54609 L it is roughly 20% larger.
Area, Speed, Pressure, and Energy
The remaining categories use the same factor method. Handy anchors: 1 acre = 43,560 ft² and 1 ha = 10,000 m² = 2.47105 acres; 1 mph = 1.60934 km/h, so 60 mph is about 96.56 km/h; 1 atm = 101,325 Pa = 14.6959 psi; 1 kcal = 4.184 kJ and 1 kWh = 3.6 million joules. The Speed Calculator handles trip math built on speed.
Master Conversion-Factor Table
The most-used pairs (exact values are definitions; others rounded as shown).
| Category | Conversion | Equivalent |
|---|---|---|
| Length | 1 inch | 2.54 cm (exact) |
| Length | 1 foot | 0.3048 m (exact) |
| Length | 1 mile | 1.609344 km (exact) |
| Weight | 1 ounce | 28.3495 g |
| Weight | 1 pound | 0.453592 kg |
| Weight | 1 kilogram | 2.20462 lb |
| Volume | 1 US gallon | 3.78541 L |
| Area | 1 acre | 43,560 ft² (exact) |
| Speed | 1 mph | 1.60934 km/h (exact) |
| Energy | 1 kcal | 4.184 kJ (exact) |
Metric Prefixes: Kilo, Centi, Milli
The metric system scales by powers of ten; the prefix gives the multiplier:
| Prefix | Symbol | Multiplier | Example |
|---|---|---|---|
| kilo | k | 1,000 | 1 km = 1,000 m |
| centi | c | 0.01 | 1 m = 100 cm |
| milli | m | 0.001 | 1 g = 1,000 mg |
| micro | µ | 0.000001 | 1 mL = 1,000 µL |
Every step is a power of ten, so metric-to-metric conversion just moves the decimal point: 1 m = 100 cm = 1,000 mm, and 1 kg = 1,000 g = 1,000,000 mg.
Short Ton vs. Long Ton vs. Metric Tonne
Three different tons circulate in commerce, and mixing them up gets expensive:
| Unit | Pounds | Kilograms | Used in |
|---|---|---|---|
| US short ton | 2,000 lb | 907.18 kg | United States |
| UK long ton | 2,240 lb | 1,016.05 kg | UK (historical) |
| Metric tonne (t) | 2,204.62 lb | 1,000 kg | Worldwide |
A metric tonne is about 10% heavier than a US short ton; the long ton and tonne differ by only about 16 kg. The t unit in this converter is the metric tonne.
Precision and Rounding Pitfalls
- Don't chain rounded results. 70 kg → 154.3 lb → kg returns 69.99 kg when you re-enter the rounded value; keep full precision between steps.
- Factors have limits. This tool stores 1 lb as 0.453592 kg versus the exact 0.45359237 kg — an error under one ten-thousandth of a percent.
- Tiny results display as zero. Anything below about 0.0000005 rounds to 0.000000 at six decimals; convert in the opposite direction instead.
- Match significant figures to the input. If a sign says 5 miles, reporting 8 km is more honest than 8.04672 km.
FAQ
Does it support temperature?
Yes. Celsius, Fahrenheit, and Kelvin use the correct formulas — °F = °C × 9/5 + 32 and its inverses — not multipliers, so 37 °C correctly becomes 98.6 °F.
How precise are the conversions?
Results show up to 6 decimal places. Core factors such as 1 in = 2.54 cm, 1 mi = 1.609344 km, and 1 gal = 3.78541 L follow international definitions.
Can I swap units quickly?
Yes. Click Swap Units to exchange the From and To selections, then Convert again for the reverse.
What is the difference between a US ton, a metric tonne, and a UK long ton?
A US short ton is 2,000 lb (about 907 kg), a metric tonne is 1,000 kg (about 2,205 lb), and a UK long ton is 2,240 lb (about 1,016 kg). The t unit here is the metric tonne.
Why does temperature use a formula instead of a conversion factor?
The scales have different zero points: 0 °C equals 32 °F. Multiplying alone would be wrong, so the formulas add or subtract the offset.
Is a US gallon the same as an imperial gallon?
No. A US gallon is 3.78541 L; the UK's imperial gallon is 4.54609 L, about 20% larger. This converter uses US customary units.
How can I convert kilograms to pounds in my head?
Multiply by 2.2, or double and add 10%. For 70 kg that gives 154 lb, versus the exact 154.3 lb from the 2.20462 factor.
Why did my conversion round to 0.000000?
The display stops at six decimals, so results below about 0.0000005 show as zero. Convert in the opposite direction, or express tiny values with the Scientific Notation Calculator.