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Unit Converter

Convert length, weight and volume units in your browser. Pick a category, type a value and the result appears at once, worked out through a fixed base unit with standard factors.

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Quick answer

Choose a category (Length, Weight or Volume), pick the 'from' and 'to' units and type a value. The converted figure appears straight away, rounded to six decimals. Each conversion goes through a base unit (metre, kilogram or litre) with fixed standard factors, so the same input always gives the same answer. Volume units are US customary (a 3.785-litre gallon), and 'ton' means the metric tonne. It all runs in your browser.

  • 3categories
  • 17units
  • 6decimal places
  • 25.4 mmone inch, exactly

What the Unit Converter does

Pick Length, Weight or Volume and the unit menus fill with that category's options; the result updates as you type. Length covers metre, kilometre, centimetre, mile, yard, foot and inch. Weight covers kilogram, gram, pound, ounce and tonne. Volume covers litre, millilitre, US gallon, US cup and cubic metre.

The answer is shown to six decimal places with trailing zeros trimmed, and the arithmetic is the same every time. Nothing is sent anywhere; the conversion happens on your device.

How it works

Each unit is stored as a factor of one base unit per category: the metre for length, the kilogram for weight and the litre for volume. To convert, the tool multiplies your value by the 'from' factor to get the base unit, then divides by the 'to' factor.

The factors come from the standard definitions: an inch is exactly 25.4 mm, a foot 0.3048 m, a yard 0.9144 m and a pound 0.45359237 kg (held here to six figures). Because every conversion passes through the base unit, any pair in a category works without a separate factor for each combination.

Data source & conversion logic

The conversion factors are the internationally agreed definitions: the 1959 international yard-and-pound agreement (inch 25.4 mm, yard 0.9144 m, pound 0.45359237 kg) for imperial length and weight, US customary definitions for volume (gallon 3.785 L, cup 236.6 mL), and the metric tonne (1,000 kg). They are constants inside the tool, so no result depends on a network call.

  1. Read the value and units. Take your number and the chosen 'from' and 'to' units within one category (Length, Weight or Volume).
  2. Convert into the base unit. Multiply by the 'from' factor to express the value in the category's base unit: metre, kilogram or litre.
  3. Convert out to the target. Divide by the 'to' factor to get the requested unit.
  4. Round and show. Round to six decimal places, trim trailing zeros and display the result as you type.

Conversion through a base unit

result = value × factor(from) ÷ factor(to) (factor = the unit's size in the category's base unit: metre, kilogram or litre)
Worked examples
5 miles → kilometres: 5 × 1609.34 ÷ 1000 = 8.0467 km
2 pounds → grams: 2 × 0.453592 ÷ 0.001 = 907.184 g
3 US gallons → litres: 3 × 3.78541 ÷ 1 = 11.35623 L

Results are rounded to six decimal places with trailing zeros removed. The mile and pound factors are held to six significant figures (true values 1609.344 m and 0.45359237 kg), so very large conversions can differ in the last digit.

Every conversion goes through a base unit

5 mi× 1609.348046.7 m÷ 10008.0467 km
Each unit only needs its size in metres, kilograms or litres, so any pair in a category converts.

Technical details

CategoriesLength, Weight, Volume
Length unitsmetre, km, cm, mile, yard, foot, inch
Weight unitskilogram, gram, pound, ounce, tonne
Volume unitslitre, millilitre, US gallon, US cup, cubic metre
MethodFactor through a base unit (metre / kg / litre)
Volume systemUS customary (not imperial)
'ton'Metric tonne, 1,000 kg
Rounding6 decimal places, trailing zeros trimmed
Where it runsIn your browser; nothing is uploaded

Standards and references

  • 1959 international yard and pound: fixes the inch at 25.4 mm, the yard at 0.9144 m and the avoirdupois pound at 0.45359237 kg. The length and weight factors come from it.
  • SI base units: the metre, kilogram and litre are the base units each conversion passes through.
  • US customary volume: the gallon (3.78541 L) and cup (236.588 mL) here are US, not imperial. A UK gallon is about 20% larger.

Accuracy and limits

Volume is US customary: the gallon is 3.785 L and the cup 236.6 mL. A UK (imperial) gallon is about 20% larger at 4.546 L, so don't use these figures for a British recipe or fuel amount.

'Ton' here is the metric tonne (1,000 kg), not the US short ton (907 kg) or the UK long ton (1,016 kg). Check which one your source means.

The mile and pound factors are held to six figures (1609.34 m, 0.453592 kg) instead of their exact values (1609.344 m, 0.45359237 kg). For everyday use the difference is tiny, but it can show in the last digit of a very large conversion.

Results round to six decimal places, so a fraction like one-third of a unit is shown rounded, not as a repeating decimal.

It covers length, weight and volume only. Temperature, area, speed, data size, pressure and time are not included. Temperature needs an offset as well as a factor, so it has its own tool.

US gallon vs UK gallon

US gallon (this tool)3.785 LUK gallon about 20% larger
If a recipe or spec is British, its gallons are bigger than the ones here.

Real-world uses

Recipes and cooking

Convert cups, millilitres and grams when a recipe comes from another country.

DIY and measuring

Switch between inches, centimetres, feet and metres for a build or a room.

Travel

Make sense of miles, kilometres, pounds and kilograms abroad.

Homework and study

Check unit-conversion answers, with the factor shown so you can work them by hand.

When it fits, and when it doesn't

Good for

  • Everyday length, weight and volume conversions
  • Quick checks where six decimals is plenty
  • US customary cooking and measuring
  • Seeing the conversion factor as well as the answer

Not the best choice for

  • Imperial (UK) gallons, pints or fluid ounces
  • Temperature, area, speed, data or pressure
  • Telling short ton, long ton and tonne apart
  • Trade or legal measurement that needs certified exactness

For temperatures, use the temperature converter, since it needs an offset rather than a factor. Imperial UK volumes and units outside length, weight and volume are not covered here.

Frequently asked questions

Which gallon and cup does it use?
US customary: the gallon is 3.78541 L and the cup 236.588 mL. A UK imperial gallon is about 20% bigger (4.546 L), so keep the two systems apart.
Is 'ton' a metric tonne or a US ton?
The metric tonne, 1,000 kg. It is not the US short ton (about 907 kg) or the UK long ton (about 1,016 kg).
How does it convert between two units?
It multiplies your value by the 'from' factor to get the category's base unit (metre, kilogram or litre), then divides by the 'to' factor.
Where do the conversion factors come from?
From the standard definitions: the 1959 international yard-and-pound agreement for length and weight, and US customary definitions for volume. They are constants in the tool, with no lookup or network call.
Why six decimal places?
That is plenty for everyday use without a long string of digits. Trailing zeros are trimmed so the answer stays readable.
Can it convert temperature?
No. Temperature scales are offset from each other (0 °C is 273.15 K), so a single ratio won't do. Use the separate temperature converter.
Does it do area, speed or data sizes?
Not at the moment. It covers length, weight and volume; area, speed, time, pressure and data size are not included.
Is the mile factor exact?
It is 1609.34 m, rounded from the exact 1609.344 m, and the pound is 0.453592 kg against the exact 0.45359237 kg. The gap shows only in the last digit of very large conversions.
Is an ounce weight or volume here?
Weight: the avoirdupois ounce, about 28.35 g. The US fluid ounce measures volume and is not offered.
Is my data sent anywhere?
No. The conversion runs in your browser with no network call.
Why does my answer differ from another converter?
Usually the other converter used imperial volume, a different kind of 'ton' or more decimal places. Check that the units and system match before comparing.
Can it convert nautical miles or light-years?
No. Length here is metre, kilometre, centimetre, mile, yard, foot and inch only.

References

The factors are the internationally agreed definitions (the 1959 yard-and-pound agreement and US customary volume), stored as constants in the page. The same input always gives the same answer, and nothing leaves your browser.

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