Unit Converter
Quickly convert length, area, mass, and volume units.
Result
0.1 cm
Common unit references are included for practical conversion needs.
Unit converter
Convert length, area, mass, volume, and speed.
Converts between common units using standard conversion factors.
- Length: mm, cm, m, km, inch, foot, mile, nautical mile, and traditional units.E.g. 1 m = 100 cm ≈ 3.28084 ft.
- Area: m², are, hectare, square feet, acre, pyeong (坪), etc.E.g. 1 pyeong ≈ 3.3058 m².
- SI units
- The International System of Units (SI) defines base units (metre, kilogram, second, ampere, etc.) and derived units used worldwide in science and trade.
- Pyeong (坪)
- Pyeong is a unit of area used in Korea and Japan; 1 pyeong ≈ 3.3058 m². It is commonly used for floor area in real estate.
What unit conversion gets wrong
Conversion looks like a lookup table until squared and cubed units appear, or until you meet two different units sharing the same name.
Squared and cubed units
1 m = 100 cm, but 1 m² = 10,000 cm². If length scales by 100, area scales by 100 squared.
Volume is cubed, so 1 m³ = 1,000,000 cm³. Applying a length factor to an area or volume is wrong by a factor of 100 or 10,000, so check the dimension before the number.
Two kinds of gallon, two kinds of ounce
A US gallon is about 3.785 L; an imperial (UK) gallon is about 4.546 L. That is a difference of more than 20%, which is enough to ruin a fuel-economy comparison.
Ounces split the same way. A fluid ounce measures volume (about 29.57 mL in the US) while an ounce measures weight (about 28.35 g). Recipes and product specs often fail to say which they mean.
Exact definitions versus approximations
Some conversions are exact by definition: one inch is exactly 2.54 cm, and one pound is exactly 0.45359237 kg. These were fixed by international agreement.
Others are approximations that vary with conditions. A litre of water weighs about a kilogram, but only near 4°C — the relationship between volume and mass depends on temperature and on the substance.
Temperature needs addition, not just multiplication
Celsius and Fahrenheit have different zero points, so you cannot convert by ratio alone: °F = °C × 9/5 + 32.
0°C is 32°F and 100°C is 212°F. Converting a temperature difference is different again: drop the +32 and multiply by 9/5 only. A rise of 10°C is a rise of 18°F, not 50°F.
Rounding at the right moment
Round once, at the end. Rounding each intermediate step compounds the error, which shows up quickly in multi-step conversions.
Also keep significant figures honest. Converting a rough 'about 5 miles' into 8.04672 km implies a precision the original measurement never had; 8 km is the truthful answer.
| Unit | Equivalent |
|---|---|
| 1 inch | 2.54 cm (exact by definition) |
| 1 foot | 30.48 cm |
| 1 mile | 1.609 km |
| 1 pound | 0.45359237 kg (exact by definition) |
| 1 US gallon | 3.785 L (imperial: 4.546 L) |
| 1 acre | 4,047 m² · 0.4047 hectares |
Frequently asked questions
- Why is 1 m² equal to 10,000 cm² and not 100?
- Area is length squared. Since 1 m = 100 cm, 1 m² = 100 × 100 = 10,000 cm². Volume is cubed, so 1 m³ = 1,000,000 cm³.
- US gallons or imperial gallons?
- They differ by more than 20% — 3.785 L versus 4.546 L. US sources mean US gallons; UK sources usually mean imperial. Check before comparing fuel economy figures.
- Is a fluid ounce the same as an ounce?
- No. A fluid ounce measures volume (about 29.57 mL in the US) and an ounce measures weight (about 28.35 g). They line up only loosely, and only for water.
- How much is a 10°C rise in Fahrenheit?
- 18°F. For a difference, multiply by 9/5 and do not add 32. The +32 only applies when converting a specific temperature.
- Does a litre of water always weigh a kilogram?
- Only approximately, and only for water near 4°C. Density changes with temperature and differs for every other substance.