Converting between metric and imperial units is one of those small daily tasks that is surprisingly hard to do in your head. A recipe from a US website calls for 2 cups of flour but your scale only shows grams. A package you ship overseas is priced by the pound while the courier quoted you per kilogram. A weather forecast tells you the high will be 24 degrees, and you cannot tell whether that means a T-shirt or a parka. This unit converter solves all of those conversions in one place — length, weight, volume, and temperature, between metric and imperial — using the exact conversion factors published by NIST, the US National Institute of Standards and Technology.
Type a value, pick the unit you are converting from and the unit you want, and the result appears instantly. Every conversion factor below is anchored to a SI base unit (the meter, the gram, and the liter), which means a 5-pound bag of apples weighs the same number of grams whether you convert it directly or go through ounces first.
How to Use
- Enter the Value you want to convert. It can be a whole number, a decimal, or zero — for example 1, 5.5, or 0.
- Choose the From Unit. The list groups naturally by measurement: length units (inch, foot, yard, mile, millimeter, centimeter, meter, kilometer), weight units (ounce, pound, gram, kilogram, US ton), cooking and liquid volume units (teaspoon, tablespoon, fluid ounce, cup, pint, quart, gallon, milliliter, liter), and temperature units (Celsius, Fahrenheit, Kelvin).
- Choose the To Unit. It must belong to the same category — you cannot turn a kilogram into a meter, because they measure different things. The converter will flag a cross-category choice with a clear error instead of printing a meaningless number.
- Read the result card. The highlighted Converted Value is your answer, and it is measured in whatever To Unit you picked — if you converted kilograms to pounds, the number is in pounds; if you converted meters to feet, it is in feet. Below it, the Conversion Factor shows exactly what you multiplied by, and the Equivalent in SI Base Unit shows the measurement in its scientific base unit (meters, grams, liters, or Celsius) so you can chain conversions yourself.
For temperature, the Conversion Factor reads 1.0 on purpose. Temperature is not a pure multiplier: Celsius and Fahrenheit sit on different scales with an offset (the 32-degree shift between freezing points), so the converter routes temperature through an affine path rather than a simple ratio. The offset is already applied inside the result, so you do not have to add or subtract anything yourself.
For temperature, negative values are expected and allowed (a cold winter day can be −10°C). For length, weight, and volume, however, a negative measurement has no physical meaning, so the converter rejects negative values with an error rather than silently producing a negative length.
The Conversion Method
Every non-temperature unit is normalized to a SI base unit with a fixed factor, then rescaled to the target unit:
result = value × factor(fromUnit) ÷ factor(toUnit)
The most important exact factors come straight from international agreement:
- Length: 1 inch = 0.0254 m exactly, 1 foot = 0.3048 m, 1 mile = 1609.344 m.
- Weight: 1 pound = 453.59237 g exactly, so 1 kilogram = 2.20462262 pounds.
- Volume (US): 1 US gallon = 3.785411784 L exactly, so 1 liter = 0.264172052 gallons.
- Temperature uses an affine path through Celsius: C = (F − 32) × 5/9, and K = C + 273.15. Water freezes at 0°C = 32°F = 273.15 K and boils at 100°C = 212°F.
That anchor design is why conversions agree with each other. Converting 10 pounds to grams gives 4535.92 g; converting 10 pounds to kilograms gives 4.53592 kg; divide the gram figure by 1000 and the numbers match exactly.
Everyday Reference Values
Keep these in your back pocket so you can sanity-check the calculator:
- A short flight of steps is about 1 meter; a tall adult male is roughly 1.8 meters, or 5 feet 11 inches.
- A loaf of sandwich bread weighs about 450 g, just about 1 pound.
- A typical bottled water is 500 mL, a little over 2 cups, or about 16.9 fluid ounces.
- Room temperature is 20–22°C, which is 68–72°F. A warm shower is around 38°C (100°F).
Examples
Example 1 — Grocery math by weight. A US supermarket lists ground beef at $4.99 per pound. Your local butcher in Europe prices the same cut at €9.50 per kilogram. Convert: 1 kg = 2.20462 lb, so the US price per kilogram works out to about $4.99 × 2.20462 ≈ $10.99 per kg. The butcher is actually cheaper once units are aligned — which is exactly why comparing prices without converting units so often misleads shoppers.
Example 2 — Fuel economy and cost. A US rental car burns 8.5 liters per 100 km on the highway, but the fuel gauge in your rental quote talks in gallons. At $3.80 per US gallon, and knowing 1 liter = 0.264172 gallons, the car uses 8.5 × 0.264172 ≈ 2.245 gallons per 100 km. A 500 km trip consumes about 11.2 gallons, or roughly $42.50 in fuel — before tax.
Example 3 — Shipping an overseas parcel. You have a 5 kg box of books. The international courier charges by the pound. 5 kg × 2.20462 = 11.0231 lb, so you will be quoted for an 11-pound parcel (rounded up by most carriers). Checking that number before you hand the box over prevents a surprise surcharge at the counter.
Example 4 — Baking from a US recipe. A cookie recipe calls for 2 cups of milk. 1 US cup = 0.236588 L, so 2 cups = 0.473176 L, or 473 mL. Pour that straight into a metric measuring jug and you are done — no guessing whether a "cup" means 200 mL or 250 mL.
Example 5 — Weather travel. You land in Berlin and the app says the afternoon high is 14°C. Convert to Fahrenheit: 14 × 9/5 + 32 = 57.2°F. That is a light-jacket day, not a beach day, which saves you from packing the wrong clothes.
Example 6 — Road distance in metric. A road sign reads 1 kilometer to the next town, but you think in miles. Because 1 mile = 1,609.344 m exactly, 1 km = 1,000 / 1,609.344 ≈ 0.6214 miles. The reverse — how many feet in a meter — uses 1 ft = 0.3048 m, so 1 m ≈ 3.2808 feet. These two anchor conversions are the ones runners and drivers reach for most.
FAQ
How do I convert kilograms to pounds?
Multiply the kilogram value by 2.20462262. For example, 5 kg = 5 × 2.20462262 = 11.0231 lb. Put 5 in the Value box, choose kilogram as the From Unit and pound as the To Unit, and the converter shows 11.0231 instantly.
How many liters are in a US gallon?
One US gallon is exactly 3.785411784 liters, which means 1 liter = 0.264172052 gallons. Note that a UK (imperial) gallon is larger — about 4.546 L — so this converter uses the US gallon, which is what US fuel, milk, and juice containers are labeled in.
Why can't I convert kilograms to meters?
Because they measure different physical quantities: kilograms measure mass, meters measure length. A conversion between them has no physical meaning. The same is true for liters to pounds, feet to Celsius, and any other cross-category pair. Pick two units from the same group — length with length, weight with weight, and so on.
How accurate are these conversion factors?
The core factors are exact by international agreement: 1 inch = 0.0254 m, 1 pound = 0.45359237 kg, and 1 US gallon = 3.785411784 L. Temperature follows the defined Celsius–Fahrenheit relationship (water freezes at 0°C / 32°F and boils at 100°C / 212°F at standard pressure). Results match NIST-published tables to at least six significant digits.
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9, divide by 5, then add 32: F = C × 9/5 + 32. For example, 20°C × 9/5 + 32 = 68°F. To go the other way, subtract 32 first, then multiply by 5/9. Negative Celsius values are perfectly valid here — they are cold temperatures, not errors.
Why does the conversion factor show 1.0 for temperature?
Because temperature uses an offset, not a multiplier. When you convert Celsius to Fahrenheit the formula is F = C × 9/5 + 32, which has both a scale (9/5) and a shift (32). The converter folds that whole affine path into the result directly, so the separate "multiply by" factor has nothing left to do and displays 1.0. The converted temperature itself is still correct — for example 20°C shows as 68°F.
Is a negative value ever allowed?
Yes, for temperature only. −10°C is a real winter temperature. For length, weight, and volume, a negative amount has no physical meaning, so the converter rejects it and asks for a value of zero or above. Zero itself is handled: converting 0 kg to pounds simply returns 0 lb.
What is the difference between a US ton and a metric tonne?
A US short ton is 2,000 pounds, about 907.18 kg. A metric tonne (tonne) is 1,000 kg, about 2,204.62 lb. The converter's "tonUS" option refers to the US short ton. When shipping heavy cargo, always confirm which ton the carrier means, because the difference is more than 10%.
Disclaimer
This unit converter is provided for informational purposes only and does not constitute professional engineering, medical, cooking, or commercial advice. Conversion factors follow NIST-published definitions for US customary units; other jurisdictions (notably the UK imperial system) use slightly different volume definitions. Always double-check critical measurements — dosages, structural loads, shipping weights, or legal quantities — against authoritative sources before acting on them.