Overview
What does this unit converter do?
ToolHub's unit converter handles nine categories of measurement in one page: length, weight, temperature, volume, area, speed, time, data (bits and bytes), and energy. Type a number into either side, and the other side updates instantly. A full table below the inputs shows your value in every unit at once, so you do not need to convert one-at-a-time.
Conversions run entirely in your browser. No data leaves your device, and the page works offline once loaded. All factors are based on the International System of Units (SI) and the US National Institute of Standards and Technology (NIST) for US customary units.
What's inside
The categories explained
Length
Millimetres, centimetres, metres, kilometres for metric; inches, feet, yards, miles for US customary; plus the nautical mile (1,852 m) used in aviation and maritime navigation. Common conversion: 1 inch = 2.54 cm exactly.
Weight (mass)
Milligrams, grams, kilograms, metric tonnes; ounces, pounds, stones, US short tons (2,000 lb), and UK long tons (2,240 lb). Important: 1 kg = 2.20462 lb, not 2.2 — the difference matters at larger weights.
Temperature
Celsius, Fahrenheit, and Kelvin. Temperature is the only category that uses both a scale factor and an offset, so the conversion formulas are not simple multiplication: °F = °C × 9/5 + 32 and K = °C + 273.15.
Volume
Millilitres, litres, cubic metres for metric. US customary includes teaspoons, tablespoons, fluid ounces, cups, pints, quarts, and gallons. UK imperial pints and gallons are also included — these are about 20% larger than US versions. Plus cubic inches and cubic feet for engineering work.
Area
Square millimetres through square kilometres, square inches through square miles, plus the acre (43,560 sq ft) and the hectare (10,000 m²). Real estate, farmland, and construction all use these regularly.
Speed
Metres per second (SI base), kilometres per hour, miles per hour, knots (nautical miles per hour), and feet per second. Knots and km/h are the most commonly confused: 1 knot = 1.852 km/h.
Time
Milliseconds through years. The "month" unit here is the standard 30-day month and "year" is 365 days; for calendar math involving specific dates, use a dedicated date calculator.
Data
Decimal (KB, MB, GB, TB, PB — powers of 1,000) and binary (KiB, MiB, GiB, TiB — powers of 1,024) units. Hard drive marketing uses decimal. RAM and operating systems usually use binary, which is why "500 GB" drives show as "465 GiB" in Windows.
Energy
Joules, kilojoules, calories (small calorie = 4.184 J), kilocalories (food Calories), watt-hours, kilowatt-hours, BTU, and foot-pounds. Watch out: the "Calorie" on a nutrition label is actually a kilocalorie.
Quick reference
Common conversions people search for
Feet to metres
1 ft = 0.3048 m. A 6 ft person is 1.83 m. A 100 ft fence is 30.48 m.
Kilograms to pounds
1 kg = 2.20462 lb. 70 kg ≈ 154 lb. 100 kg ≈ 220 lb.
Celsius to Fahrenheit
°F = °C × 1.8 + 32. 20°C = 68°F. 30°C = 86°F. 100°C = 212°F (boiling).
Litres to US gallons
1 L = 0.264 US gal. A 50 L tank is 13.2 US gallons (or 11.0 UK gallons).
Acres to square metres
1 acre = 4,047 m² ≈ 0.405 hectares. A standard US football field is about 1.32 acres.
Miles per hour to kilometres per hour
1 mph = 1.609 km/h. 60 mph = 96.6 km/h. 100 mph = 160.9 km/h.
Megabytes to mebibytes
1 MB = 1,000,000 bytes. 1 MiB = 1,048,576 bytes. So 1,000 MB ≈ 954 MiB.
Calories to kilojoules
1 kcal = 4.184 kJ. A 2,000 calorie diet ≈ 8,368 kJ per day.
Precision
Why the answers may differ from other calculators
Different sources use slightly different conversion factors, often due to rounding at the third or fourth decimal. ToolHub uses the official factors:
- 1 inch = 2.54 cm exactly (international standard since 1959)
- 1 lb = 0.45359237 kg exactly (international avoirdupois pound)
- 1 US gal = 3.785411784 L exactly
- 1 acre = 4046.8564224 m² exactly
- 1 BTU = 1055.06 J (international table value)
For most everyday use the difference is irrelevant. For engineering or legal work, double-check against your standard of reference (ASTM, ISO, BIPM).
Behind the scenes
Privacy and how it runs
Everything runs locally
Common questions
What is the difference between weight and mass?
In physics, mass is the amount of matter in an object (kilograms), while weight is the force gravity exerts on that mass (newtons). Everyday speech uses "weight" to mean mass. Our converter follows everyday usage: when you convert "pounds" to "kilograms" you are converting mass.
Why is there a difference between US and UK gallons?
The US gallon (3.785 L) was based on the old English wine gallon. The UK switched in 1824 to the imperial gallon (4.546 L), defined as 10 pounds of water at 62°F. The US kept the older definition. A US pint is 16 US fluid ounces; a UK pint is 20 UK fluid ounces. Recipes from either country need careful unit checking.
How is 1 second defined?
Since 1967, the second has been defined as 9,192,631,770 periods of radiation from the cesium-133 atom. This is the most precisely defined unit in the SI system.
Are kilometres always 1,000 metres?
Yes. All SI prefixes are exact powers of ten: kilo = 1,000, mega = 1,000,000, milli = 0.001, micro = 0.000001. This is unlike data, where "kilobyte" sometimes means 1,000 bytes and sometimes 1,024 (KiB).
How accurate is the temperature conversion?
The Celsius–Fahrenheit and Celsius–Kelvin formulas are exact. The only error comes from your input precision. We display up to 10 significant digits.