Unit Converter — Free Length, Weight, Temperature & More

How Unit Conversion Works

Almost every conversion on this page follows the same simple rule: Result = Value × (From-unit factor ÷ To-unit factor). To convert miles to kilometers you multiply by 1.609344; to go the other direction you divide by the same number. That is all the converter above is doing behind the scenes — it looks up the exact factor for each unit and applies it instantly, so you can also use these factors by hand with a pocket calculator.

Temperature is different because the scales do not share a zero. Water freezes at 32°F but 0°C, so converting between them requires an offset as well as a scale change: °F = (°C × 9/5) + 32 and °C = (°F − 32) × 5/9. Kelvin needs only an offset from Celsius: K = °C + 273.15. Because of that offset, temperature is the only common conversion you cannot do with multiplication alone.

How to Use the Unit Converter

1. Pick a category — Length, Weight, Temperature, Volume, Area, Speed or Time.
2. Type your value in the Value box. The result appears instantly — there is no submit button.
3. Choose the units to convert from and to. Use the ⇆ button to swap them in one tap.
4. Read the formula under the result to see exactly how the conversion was calculated.

Conversion Formulas & Exact Factors

Every conversion on this page uses internationally defined conversion factors. The general rule is simple:

Result = Value × (From-unit factor ÷ To-unit factor)

Length (base: meter)

Weight / Mass (base: kilogram)

Temperature

Volume (base: liter)

Area, Speed & Time

Worked Examples

Popular Conversions

These are the conversions people search for most often — all supported above:

Quick-Reference Conversion Tables

The most-searched conversions on the web, answered in one line each. Use the converter above for exact values — these factors are the ones people actually look up.

Length

Weight / Mass

Temperature (anchor points)

Volume

Area

Speed

Time

Conversion Formulas — One-Line Cheat Sheet

Every formula the converter uses, on one line each — handy for homework, exams and quick mental math.

US Customary vs Imperial vs Metric — What’s the Difference?

Metric (SI) is the decimal-based international system — meters, kilograms, liters — used officially almost everywhere. US customary is what Americans use in daily life — feet, pounds, US gallons. Imperial is the older British system the US customary system grew out of; Britain itself now mostly uses metric, but imperial units linger in pubs (pints) and road signs (miles).

Practical advice: an American recipe means the US cup (236.6 mL); Australian and many Asian recipes often mean the metric cup (250 mL) — about 6% larger, enough to throw off baking. Fuel economy and tank sizes quoted in gallons are US gallons in the States and imperial gallons in older British sources — always check which one a figure uses before converting. This converter uses US customary units, the standard for American recipes, road signs and fuel measurements.

Why the US Still Uses Imperial Units

The United States, Liberia and Myanmar are the only countries not officially on the metric system. The reason is not technical — it is historical and economic.

In 1975, Congress passed the Metric Conversion Act, but it made metrication voluntary rather than mandatory. With no legal deadline, the enormous cost of converting road signs, machinery, building codes and manufacturing tooling — combined with simple cultural habit — kept customary units in everyday American life.

Ironically, US customary units are themselves defined in metric: since the 1959 International Yard and Pound Agreement, 1 inch is exactly 2.54 cm and 1 pound is exactly 0.45359237 kg. American science, medicine, the military and most manufacturing already work in metric — it is daily life (road signs, weather reports, grocery labels) that stayed customary. So converting between the two is really just translating one exact definition into another.

Everyday Conversions by Use Case

Cooking & Baking

US recipes use cups, tablespoons and Fahrenheit; most of the world uses milliliters, grams and Celsius. Remember: 1 US cup = 236.6 mL, 1 tablespoon = 14.8 mL, 1 teaspoon = 4.9 mL, and a 350°F oven is 177°C. Watch out for the metric cup (250 mL) in Australian and many Asian recipes — it is about 6% larger than a US cup, and that difference matters in baking.

Driving & Travel

US speed limits are posted in mph; much of the world drives in km/h. A 65 mph limit is about 105 km/h, and a 70 mph cruise is 113 km/h. Fuel economy flips too: 30 miles per US gallon equals about 7.8 L/100 km (divide 235.2 by the mpg figure). Road distances: 100 miles is 161 km.

Fitness & Body Weight

Gym weights and body-weight goals in the US are tracked in pounds; most fitness science uses kilograms. A 150 lb person is 68 kg; a 225 lb bench press is 102 kg. Runners straddle both worlds: a marathon is 26.2 miles, which is 42.2 km, and a 5K is 3.1 miles.

Weather

US forecasts speak Fahrenheit; most of the world uses Celsius. Anchor on four points and you will never be lost: 32°F = 0°C (freezing), 68°F = 20°C (pleasant room temperature), 98.6°F = 37°C (body temperature), 212°F = 100°C (boiling). A quick mental shortcut: double the Celsius and add 30 for a rough Fahrenheit (± a few degrees near room temperature).

Home & DIY

US tape measures read feet and inches; flat-pack furniture and most tools sold globally are metric. A 6 ft person is 1.83 m; an 8 ft ceiling is 2.44 m. For flooring and paint, convert the area, not the length: 500 ft² is 46.5 m² — multiplying feet by 0.3048 only works for distances.

Metric Prefixes at a Glance

Metric units scale by powers of ten — learn these eight prefixes and you can read any metric unit, from nanometers to kilometers.

How Accurate Is This Converter?

This converter uses the exact internationally defined factors — 1 inch is precisely 2.54 cm, 1 pound is precisely 0.45359237 kg — so its results agree with scientific references and standard conversion tables to the displayed precision. Temperature uses the exact defining formulas, and results are shown to a sensible number of digits rather than misleading pseudo-precision.

For everyday cooking, travel, fitness, homework and DIY, this accuracy is more than enough. For certified engineering, legal-for-trade or medical dosing work, always use calibrated instruments and the standards required by your regulator — an online converter is a convenience tool, not a certification.

Unit Converter FAQs