How to use the feet and inches converter
Architects move between imperial and metric all the time: a US client's ceiling height against a European product sheet, a 4 × 8 sheet against a 600 mm grid, a survey in decimal feet against a plan drawn in feet and inches. This converter does all of those at once and rounds back to the fractions people actually measure with.
- Choose what you are converting from: feet, inches and a fraction, decimal feet, inches, millimetres, centimetres or metres.
- Enter the measurement. For feet and inches, type the feet and inches and pick a fraction from the list. Inches above 12 are fine; they carry into feet.
- Pick the rounding you want for the feet-and-inches result, from 1/2 inch down to 1/64 inch.
The results show the measurement in architectural feet and inches, decimal feet, inches, millimetres, centimetres and metres, plus how far the rounded fraction is from the exact value.
Conversion formulas
Total inches = Feet × 12 + Inches + Fraction
Millimetres = Inches × 25.4
Decimal feet = Inches ÷ 12
Fraction = round(decimal part of inches × 16) ÷ 16, for 1/16" rounding
The inch has been defined as exactly 25.4 mm since 1959, so these conversions are exact until you round. All of the error comes from the fraction step, which is why the result shows it.
| Imperial | Metric |
|---|---|
| 1/16" | 1.5875 mm |
| 1/8" | 3.175 mm |
| 1/4" | 6.35 mm |
| 1/2" | 12.7 mm |
| 1" | 25.4 mm |
| 1'-0" | 304.8 mm |
| 8'-0" | 2,438.4 mm |
| 1'-11 5/8" | about 600 mm |
| 3'-3 3/8" | about 1,000 mm |
Worked examples
5' 7 3/8" to millimetres
5 feet is 60 inches, plus 7 inches, plus 3/8 = 0.375, gives 67.375 inches. Multiplying by 25.4 gives 1,711.3 mm, or 1.711 m. In decimal feet it is 67.375 ÷ 12 = 5.615 ft.
2,400 mm to feet and inches
A 2,400 mm ceiling height is 2,400 ÷ 25.4 = 94.488 inches. That is 7 feet (84 inches) and 10.488 inches. 0.488 × 16 = 7.8, which rounds to 8 sixteenths, or 1/2. The answer is 7'-10 1/2", only about 0.3 mm off the exact value.
12.35 decimal feet from a survey
A setback dimension of 12.35 ft is 12 feet plus 0.35 × 12 = 4.2 inches. 0.2 × 16 = 3.2, which rounds to 3/16. On the plan it becomes 12'-4 3/16". Writing it as 12'-3 1/2" by reading .35 as inches would be wrong by more than half an inch.
Who this converter helps
- Architects working on international projects or specifying metric products in imperial drawings, or the other way round.
- Interior designers checking furniture, appliances and fixtures listed in centimetres against rooms measured in feet.
- Contractors and joiners turning drawing dimensions into tape-measure fractions.
- Engineers and surveyors converting decimal feet from survey data into feet and inches.
- Architecture students learning to read and draw in both systems.
Tips for working in two unit systems
- Agree on one primary unit for a project and show the other as a reference, rather than mixing both in one dimension string.
- Round only at the end. Convert exact values, add them up, and then round the total to a fraction.
- To measure off a drawing at scale, use the architectural scale converter, and for room areas in ft² or m² use the square footage calculator.
- Riser and tread sizes are a common place for rounding errors; check them with the stair calculator.
- Metric panel products are rarely exact conversions of imperial sheets; a 1,200 × 2,400 mm board is about 3/4 inch smaller each way than a 4 × 8.
Have a floor plan with dimensions? Turn it into a 3D view the client can understand with Floor Plan to 3D.
