Metric and Imperial Measurements for DIY
By the TapeMeasureCalc team · Updated · 7 min read
Follow a project video from another country and the units stop lining up. A gallon in Ohio isn’t a gallon in Leeds, a ton in Texas isn’t a tonne in Melbourne, and a 2×4 isn’t 2 inches by 4. Here are the differences that actually catch people out, and the conversions worth keeping in your head.
Who uses what
- United States: feet and inches, square feet, cubic yards for bulk materials, US gallons, pounds and US (short) tons.
- United Kingdom: officially metric for building materials: millimetres on drawings, metres, cubic metres, litres and tonnes. Feet and inches still turn up in conversation and some room descriptions.
- Canada: a genuine mix. Lumber and many building products use imperial sizes, while plenty of products and plans are metric. Check each label.
- Australia: metric throughout. Concrete by the cubic metre, timber in millimetres, paint in litres.
Gallons: US and imperial are different
A US gallon is 3.785 litres. An imperial (UK) gallon is 4.546 litres, about 20% bigger. UK paint is sold in litres these days, so you’ll mostly meet the imperial gallon in older references and fuel economy figures.
If a US source says a gallon of paint covers 350 sq ft, that’s per US gallon. Converted, it’s about 8.6 m² per litre.
Tons and tonnes
| Unit | Pounds | Kilograms |
|---|---|---|
| US (short) ton | 2,000 | 907 |
| Metric tonne | 2,205 | 1,000 |
| Imperial (long) ton | 2,240 | 1,016 |
Nominal timber sizes
North American dimensional lumber is named by its rough-sawn size, then dried and planed smaller. A 2×4 is actually about 1½ × 3½ inches, a 2×6 about 1½ × 5½, and a 1×6 fence board about ¾ × 5½. That’s why the fence calculator uses 5½ inches for a typical picket.
In the UK and Australia, timber is sold by its metric section, such as 47 × 100 mm or 90 × 45 mm, and “planed” sizes are again a little smaller than sawn ones. Measure a piece before you build a cutting list around it.
Sheet sizes are close, not equal
A US 4 × 8 ft sheet is 1219 × 2438 mm. A standard metric sheet is 1200 × 2400 mm. The metric sheet is about 2 cm narrower and 4 cm shorter. That’s not much, but it means framing set out for one won’t line up perfectly with the other, and a sheet count from a US guide will be slightly low for metric boards.
Conversions worth remembering
- 1 inch = 25.4 mm (exactly)
- 1 foot = 0.3048 m (exactly); 1 m ≈ 3.28 ft
- 1 m² ≈ 10.76 sq ft
- 1 m³ ≈ 35.3 ft³ ≈ 1.31 yd³; 1 yd³ ≈ 0.76 m³
- 1 ft³ ≈ 28.3 litres
- 1 kg ≈ 2.2 lb
Let the calculators convert
Every calculator on this site takes both systems, field by field, and shows results in both. The cubic feet calculator has a quick converter for any volume, the square footage calculator shows square feet, square metres and square yards, and the gravel calculator gives weight in US tons and tonnes side by side.