How to use the unit converter
Choose what you're converting, type a value and choose its unit. You'll see it converted into all the other common metric and imperial units straight away. Use Share to send someone a link with your conversion filled in.
Handy construction conversions
| From | To | Multiply by |
|---|---|---|
| Feet | Metres | 0.3048 |
| Inches | Millimetres | 25.4 |
| Square feet | Square metres | 0.0929 |
| Square yards | Square metres | 0.8361 |
| Cubic yards | Cubic metres | 0.7646 |
| UK gallons | Litres | 4.546 |
| Pounds | Kilograms | 0.4536 |
| UK tons | Tonnes | 1.016 |
Slopes, pitches and falls
Slopes can be written in several ways. Roof pitches are usually given in degrees, drainage and paving falls as 1 in x or mm per metre, and ramps as a percentage or ratio.
Percent = tan(angle) × 100
1 in x = 1 ÷ tan(angle)
mm per metre = tan(angle) × 1000
| Use | 1 in x | mm/m | % | Degrees |
|---|---|---|---|---|
| Gutter fall | 1:600 | 1.7 | 0.17% | 0.1° |
| Patio fall | 1:80 | 12.5 | 1.25% | 0.72° |
| 100mm foul drain | 1:40 | 25 | 2.5% | 1.43° |
| Wheelchair ramp (max., short) | 1:12 | 83 | 8.3% | 4.76° |
Worked examples from real jobs
- Patio fall: a 4m-deep patio laid at 1 in 80 must drop 4,000 ÷ 80 = 50mm from the house to the far edge. Enter 80 as "1 in x" to see it is 12.5mm per metre. The patio calculator covers the slabs and sub-base.
- Skip sizes: skips are still sold in cubic yards. An 8-yard skip is 8 × 0.7646 = 6.1m³. The skip size calculator matches your waste to a skip.
- An old plan in feet: a 14ft × 11ft room is 4.27m × 3.35m. Converted properly that's 14.3m², not 154 ÷ 10 = 15.4m², the common shortcut that overestimates by about 8%.
- Roof pitch: a 35° roof is a 70% slope. Every metre across rises 700mm, and the sloping roof surface is about 1.22 times its plan size. The roof tile calculator uses this to find the true roof area.
Traps with UK building units
- Tons and tonnes. A metric tonne is 1,000kg, a UK (long) ton is 1,016kg and a US (short) ton is 907kg. Merchants sell aggregates by the metric tonne.
- UK and US gallons. A UK gallon is 4.546 litres, a US gallon only 3.785. American paint and concrete figures often use US gallons.
- "8 by 4" sheets. Imperial 8ft × 4ft sheets are 2440 × 1220mm. Metric plasterboard is 2400 × 1200mm. The 40mm difference matters when you're matching stud centres.
- Nominal timber sizes. A "4 by 2" is usually sold as 47 × 100mm sawn, or 38 × 89mm planed CLS. Check the actual size before planning a frame.
- Bag weights. Cement used to come in 50kg (about 1cwt) bags. Today's bags are 25kg, so halve any old "bags per job" figure.
Need an area rather than a conversion? Use the square metre calculator. For volumes of concrete in m³ and bags, use the concrete calculator.