Feet and Inches Calculator

This feet and inches calculator works the way a tape measure reads — feet, inches, and fractions. Add several runs, subtract cut lengths, multiply a board by quantity, divide a wall into equal spaces with mark positions, or convert any value to decimal feet, decimal inches, or metric.

Reviewed and updated June 30, 2026

Use it when you want to know

Add several measurements at onceStack multiple tape-measure values with proper 12-inch carry, not just two at a time.
Divide a length into equal spacesGet every cumulative mark position to lay out balusters, shelves, stair risers, or pickets.
Convert any format instantlySee feet-inches-fraction, decimal feet, decimal inches, and millimeters all at once.

Calculator

Calculate feet, inches, and fractions

Type the values the way they read off a tape measure. Add several runs, subtract a cut length, multiply a board by quantity, divide a span into equal spaces, or convert any value to decimal feet, decimal inches, or metric. Every result lands on a real tape-mark fraction.

Guide

How to calculate with feet, inches, and fractions

US construction and carpentry live on tape measures, not spreadsheets. Imperial units like feet, inches, and fractions are how walls, boards, and stair parts are still measured on site. This guide explains the normalization step every construction calculator uses, how to pick rounding precision, and the two field layouts that break most often: equal spacing and decimal-foot readback.

Why feet, inches, and fractions

A wall is 8′ 2 3/16″, not 98.1875 inches. Tape measures are marked in halves, quarters, eighths, and sixteenths, so working in fractions keeps every reading on a real mark. Decimal inches are exact for math but useless on the material — you cannot find 0.1875″ on a tape. Construction calculators convert everything to inches internally, then snap the answer back to the nearest fraction for layout.

Normalization formulainches = (feet × 12) + inches + (numerator ÷ denominator)

Every row is normalized to total inches, math is run in decimals, and the final number is formatted back to feet-inches-fraction. One foot equals exactly 12 inches (NIST SP 330, from the 1959 International Yard and Pound Agreement), so this step introduces no rounding.

Worked example: adding three runs

Say a wall has three runs at 5′ 8 7/8″, 6″, and 2′ 4 1/4″. Convert each to inches: 68.875″, 6″, and 28.25″. Sum is 103.125″. Carry back: 103 ÷ 12 = 8 feet remainder 7.125″, which rounds to 7 1/8″ at 1/16 precision. Answer: 8′ 7 1/8″. The carry is where most people make mistakes by hand, so the calculator does it automatically.

Worked example: dividing a wall into equal spaces

A 12′ 4″ wall needs 5 equal baluster spaces. Total is 148″. 148 ÷ 5 = 29.6″ per space. Back to feet-inches-fraction at 1/16: 2′ 5 5/8″ (true value 2′ 5.6″). Turn on show mark positions to get 0, 2′ 5 5/8″, 4′ 11 3/16″, 7′ 4 13/16″, 9′ 10 3/8″, and 12′ 4″ — the six marks you lay on the board, including both ends.

Matching CAD or survey decimal feet

Civil plans and survey stakes in the US use decimal feet. To check a plan dimension against your tape, switch to Convert mode, enter the decimal-feet value, and read the feet-inches-fraction output. Example: 5.2917 ft → 5′ 3 1/2″. Use a finer precision (1/32 or 1/64) only when the plan calls for it.

Common mistakes

Forgetting the 12-inch carry. Adding 68″ and 8″ gives 76″, which is 6′ 4″ — not 6′ 8″. The same trap shows up subtracting: 5′ 3″ minus 2′ 8″ is 2′ 7″ after borrowing one foot, not 3′ 5″. Hand math slips here, so the calculator carries automatically.
Using a scalar as a length. Multiplying 5′ 3″ by 4 means four copies of 5′ 3″. Do not type 4′ — the multiplier is a plain count, not a measurement.
Finer precision than your tape. Picking 1/32 when your tape only marks 1/16 gives numbers you cannot transfer to the wood. Match the tape.
Trusting rounded marks on long divisions. When 148 ÷ 5 rounds, each mark carries a tiny residual. Check the last mark against the far end before committing to cuts — if it does not land on the end, redistribution is needed.

FAQ

Feet and inches calculator questions

How do I add feet and inches with fractions?

Convert each measurement to total inches (feet × 12 + inches + numerator ÷ denominator), add the totals, then carry one foot for every 12 inches back into the result. Example: 5′ 8 7/8″ + 6″ = 68.875″ + 6″ = 74.875″ = 6′ 2 7/8″. This calculator handles the carry automatically and shows the answer rounded to your chosen fraction precision.

How do I divide feet and inches into equal spaces?

Convert the total length to inches, divide by the number of spaces, then convert each spacing back to feet-inches-fraction. Example: 12′ 4″ ÷ 5 = 148″ ÷ 5 = 29.6″ = 2′ 5 5/8″ per space. Use Divide into N mode to also see cumulative mark positions (0, 1 space, 2 spaces, … up to N) so you can lay them straight onto the board.

How do I convert feet and inches to decimal feet?

Divide total inches by 12. Example: 5′ 3 1/2″ = 63.5″ ÷ 12 = 5.2917 ft. Decimal feet is what CAD software, surveying, and civil plans in the US use, so this conversion is useful when matching a printed dimension to a plan.

How do I convert decimal feet back to feet and inches?

Take the whole-number part as feet. Multiply the decimal remainder by 12 to get inches, then round the inch fraction to your tape precision. Example: 5.2917 ft → 5 ft, then 0.2917 × 12 = 3.5″ = 3 1/2″, giving 5′ 3 1/2″. Use Convert mode with a decimal-feet input to do this in one step.

What rounding precision should I use for construction?

Most standard tape measures mark every 1/16″, so 1/16 is the safest default for framing and general layout. Use 1/8″ for rough layout, 1/4″ for concrete or gravel work, and 1/32″ or 1/64″ only for finish carpentry, cabinetry, or checking against machine-cut parts. Picking finer precision than your tape can mark produces numbers you cannot transfer to the material.

Can I multiply a measurement by a quantity?

Yes. Multiply mode takes one length and a plain count, and returns a length. Use it for total board length when you need 14 studs at 7′ 3 1/2″ each, or 8 risers at 7 5/8″ each. Do not add foot or inch marks to the multiplier — it is a count, not a measurement.

What is the difference between decimal feet and decimal inches?

Decimal feet expresses a length as a single number in feet (5.2917 ft). Decimal inches expresses the same length as a single number in inches (63.5 in). Both are exact — they only differ by a factor of 12. Decimal feet is common on civil plans and survey stakes; decimal inches is common for shop drawings and short-part cut lists.

How do I mark equal spacing on a board?

In Divide into N mode, turn on Show mark positions. The calculator lists 0, one space, two spaces, and so on up to N, each in feet-inches-fraction. Transfer them onto the material, then check the final mark against the far end to confirm the layout closed cleanly.