Construction Calculator guide
Construction Calculator: Feet, Inches and Fractions
Use our construction calculator to add, subtract, multiply and divide feet, inches and fractions, work out areas and convert to millimetres and metres.
By the AllCalculator editorial teamUpdated 15 October 20261 min read
Builders, joiners and DIYers in the UK still often work in feet and inches, especially with timber, older houses and imported plans. Adding 12′ 6½″ to 4′ 9¾″ in your head isn't easy. Our Construction Calculator does it for you, and converts to metric.
How to use the calculator (Construction Calculator)
- Choose the calculation: add, subtract, multiply, divide into equal parts, area or convert.
- Enter length A (and length B if needed).
- Choose how precisely to round: to the nearest 1/8″, 1/16″ or 1/32″.
Typing lengths
You can type lengths in several ways:
- 12' 6 1/2" for 12 feet 6½ inches
- 6ft 3in
- 3/4" for three-quarters of an inch
- 2.5m, 450mm or 30cm for metric lengths
A number with no units is read as inches.
A worked example
With the calculator's default settings, 12′ 6½″ + 4′ 9¾″:
- Inches: 6½ + 9¾ = 16¼, which is 1′ 4¼″
- Feet: 12 + 4 + 1 = 17
- Total: 17′ 4¼″, or about 5.29m
Choose Area to multiply the same two lengths: about 60.4 square feet, or 5.6m².
Handy conversions
- 1 inch = 25.4mm exactly
- 1 foot = 304.8mm
- 1 metre ≈ 3′ 3⅜″
- 1 square metre ≈ 10.76 square feet
For areas in metric, try our Square Meter Calculator. For materials, see our Concrete Calculator, Aggregate Calculator and Plasterboard Calculator.
Frequently asked questions
How do I divide a length into equal parts?
Choose divide, enter the length and the number of parts. For example, 8′ divided by 3 is 2′ 8″.
Why round to 1/16″?
It's the usual precision on a tape measure. Choose 1/32″ for finer work.
Can I mix feet and metres?
Yes. Each length can be in either, and the answer is shown in both.
Measure twice, cut once, and use the Construction Calculator for the sums in between.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.