How to use this calculator
- 1Choose what you are converting: length, area, land, volume, liquid, weight or power.
- 2Type the number you have.
- 3Pick its unit from the menu next to the box — for example inches, square feet or UK gallons.
- 4Read the answer in every other unit. The usual metric and imperial units are shown at the top.
The formula
- 01Value in the new unit = value × size of the old unit ÷ size of the new unit
- 021 inch = 25.4 mm · 1 foot = 12 in = 0.3048 m · 1 yard = 3 ft = 0.9144 m
- 031 ft² = 0.09290304 m² · 1 yd³ = 27 ft³ = 0.764554857984 m³
- 041 acre = 43,560 ft² = 4,046.86 m² · 1 hectare = 10,000 m² · 1 kanal = 20 marla
- 051 US gallon = 231 in³ = 3.785411784 L · 1 UK gallon = 4.54609 L
- 061 pound = 0.45359237 kg · 1 US ton = 2,000 lb
- 071 BTU/h ≈ 0.29307 W · 1 ton of cooling = 12,000 BTU/h ≈ 3.517 kW
Since 1959 the inch, foot, yard and pound have been defined exactly in metric units, so conversions such as 1 in = 25.4 mm and 1 lb = 0.45359237 kg are exact, not rounded. The US gallon is defined as exactly 231 cubic inches, which makes it exactly 3.785411784 litres, and the UK gallon is defined by law as exactly 4.54609 litres. The converter works from these definitions and only rounds the answer you see.
Areas and volumes use the length factor squared or cubed. Because 1 ft = 0.3048 m, 1 ft² = 0.3048 × 0.3048 = 0.09290304 m², and 1 ft³ = 0.3048³ ≈ 0.0283 m³. A common mistake is to multiply square metres by 3.28 (the length factor) — the right factor for area is 10.764.
Two units cause most mix-ups on building and garden jobs: the gallon (US 3.785 L, UK 4.546 L) and the ton (US 2,000 lb, UK 2,240 lb, metric tonne 1,000 kg ≈ 2,205 lb). Heating and cooling power uses the International Table BTU, so 1 kW is about 3,412 BTU per hour.
Worked example
1 ft is exactly 0.3048 m, because a foot is 12 inches and an inch is defined as exactly 25.4 mm.
Tips before you buy
- Type feet and inches straight into a length box: 5' 6" and 5 ft 6 in both work, and so do fractions like 3/8.
- For areas never use the length factor: 1 m² is 10.76 ft², not 3.28 ft².
- Check which gallon a product uses. US products use US gallons; older British recipes and some UK fuel figures use imperial gallons.
- When you use a converted figure to order materials, round the final quantity up, not down.
- Air conditioners sold in Europe often show both kW and BTU/h. Use the power setting here to compare them with US models.
Frequently asked questions
How many centimetres are in an inch?
Exactly 2.54 cm (25.4 mm). To turn inches into centimetres multiply by 2.54; to turn centimetres into inches divide by 2.54.
How do I convert square metres to square feet?
Multiply by 10.7639. A 20 m² room is about 215.3 ft². To go back, divide square feet by 10.7639 (or multiply by 0.0929).
How many square feet is a marla?
272¼ ft² (about 25.3 m²) in revenue measure, where 160 marla make an acre, but 225 ft² (about 20.9 m²) in many housing schemes. A kanal is 20 marla: 5,445 ft² or 4,500 ft². So a "5 marla" plot is 1,361 ft² by revenue measure or 1,125 ft² in a scheme that uses 225 ft².
How many litres are in a gallon?
A US gallon is 3.785 L and a UK (imperial) gallon is 4.546 L. So 5 US gallons is about 18.9 L, while 5 UK gallons is about 22.7 L.
How many pounds are in a kilogram?
About 2.2046 lb. A 25 kg bag of cement or plaster weighs about 55.1 lb, and a 50 lb bag is about 22.7 kg.
How many BTU per hour is 1 kW?
About 3,412 BTU/h. A 3.5 kW air conditioner is roughly 12,000 BTU/h, which is also called one "ton" of cooling.
What's the difference between a ton and a tonne?
A tonne (metric ton) is 1,000 kg, about 2,205 lb. A US ton (short ton) is 2,000 lb (907 kg) and a UK long ton is 2,240 lb (1,016 kg). When a supplier quotes "tons", ask which one they mean.
Also searched as: metric to imperial converterfeet to meters converterinches to cmgallons to litreskg to lbssquare feet to square meters
Sources
- NIST Handbook 44, Appendix C – General tables of units of measurement (exact inch, foot, pound and US gallon)
- NIST SP 811, Appendix B.8 – conversion factors (BTU per hour, ton of refrigeration, imperial gallon)
- UK Weights and Measures Act 1985, Schedule 1 (gallon = 4.54609 litres)
- NIST – Revised unit conversion factors: 1 acre = 43,560 ft² = 4,046.856 422 4 m²
- DHA Lahore Construction & Development Bye-laws 2026: marla = 25 square yards or 225 ft², kanal = 20 marla = 4,500 ft²
- How Many? A dictionary of units of measurement (UNC): the marla, standardised under British rule as the square rod, 272¼ ft²
Formulas last reviewed: September 30, 2026 ·How we check our formulas