Feet and inches calculator

Add or subtract lengths in feet, inches and fractions, and convert between feet and inches and millimetres, centimetres or metres, rounded to the nearest 1/16 inch. An inch is exactly 25.4 mm.

Sources: NIST SP 811, Appendix B.

Feet and inches calculator

Add or subtract feet, inches and fractions, or convert between feet and inches and millimetres, centimetres or metres. Conversions round the way the MeisterCalc app does.

This calculator needs JavaScript, which is turned off or didn't load. You can still do it by hand: inches = feet × 12 + inches, and an inch is 25.4 mm. The method and worked examples below give the same answers.

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Worked example: adding two lengths, then 3000 mm

  • 5' 7 3/4" is 60 + 7.75 = 67.75 in, and 2' 9 1/2" is 24 + 9.5 = 33.5 in.
  • Together: 67.75 + 33.5 = 101.25 in, which is 8 ft (96 in) and 5.25 in: 8' 5 1/4".
  • 3000 mm ÷ 25.4 = 118.11 in, which is 9 ft and 10.11 in. 0.11 × 16 = 1.8, rounded to 2/16, so 9' 10 1/8".

How it works

  • Each length becomes inches: feet × 12 + inches + the fraction.
  • The inches are added or subtracted exactly, and only the answer is rounded.
  • Back to feet: divide by 12; the remainder is the inches. The fraction is rounded to the nearest 1/16 (or 1/8 or 1/32) and reduced, so 8/16 reads 1/2.
  • Metric: mm = inches × 25.4, exactly. A foot is 304.8 mm.

Feet & Inches in MeisterCalc

Questions

How many mm in an inch?

25.4, exactly. A foot is exactly 304.8 mm.

What is 1000 mm in feet and inches?

1000 ÷ 25.4 = 39.37 in, which is 3' 3 3/8" to the nearest sixteenth.

How do I convert decimal feet to feet and inches?

Keep the whole feet and multiply the decimal part by 12: 8.4375 ft is 8 ft and 0.4375 × 12 = 5.25 in, so 8' 5 1/4".

Sources

Building rules are set by the National Construction Code, the NZ Building Code or the Approved Documents and by your council, not by this page or the app.

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