Feet and Inches Calculator

A common mistake is treating fractions as decimals: 1/2" is 0.5", but 1/4" is 0.25". Mixing fractional math with decimal math without conversion produces errors. A feet and inches calculator handles this correctly by keeping the base-12 foot and the base-2 fraction chain intact. You can do arithmetic on mixed feet-and-inches measurements quickly and trust the answer.

Select an operation: addition (+), subtraction (−), multiply length × number, multiply length × length (area), divide length ÷ number (equal parts), or divide length ÷ length (how many fit). Enter the first measurement in feet and inches. For the second measurement, enter feet and inches, or a number if multiplying or dividing. Set decimal places from 0 to 4. Choose fractional precision: whole inches, 1/2", 1/4", 1/8", 1/16", 1/32", or 1/64". Toggle calculation steps and metric conversions on or off. Click Calculate. The calculator carries inches of 12 or more into the feet box automatically.

If you enter an inches value like 7 3/8, the parser reads it correctly. You can also type 7.375 or just 3/8. The same parser rejects unparseable text and alerts you.

The calculator displays the result in multiple formats. The primary output is feet and inches, like 9' 3". Below that, total inches shows the whole length in inches. The fractional format rounds to the selected precision, for example, 9' 3 1/4" if you chose 1/4" precision. Metric conversions show meters and centimeters directly, using the exact conversion factor 1 inch = 2.54 cm from NIST SP 811.

For area results (length × length), the display changes to square feet and square inches. For counts (length ÷ length), it shows how many whole pieces fit and the leftover inches.

Adding feet and inches means adding feet to feet and inches to inches. If inches total 12 or more, you carry 12 inches as 1 foot. Subtracting means subtracting feet from feet and inches from inches. If inches go negative, you borrow 1 foot (12 inches) from the feet column.

Add 5' 8" and 3' 7"

Convert to total inches: 5' 8" = (5 × 12) + 8 = 60 + 8 = 68 inches. 3' 7" = (3 × 12) + 7 = 36 + 7 = 43 inches. Add: 68 + 43 = 111 inches. Convert back: 111 ÷ 12 = 9 feet with a remainder of 3 inches. Result: 9' 3".

Subtract 2' 8" from 5' 3"

Convert to total inches: 5' 3" = 60 + 3 = 63 inches. 2' 8" = 24 + 8 = 32 inches. Subtract: 63 − 32 = 31 inches. Convert back: 31 ÷ 12 = 2 feet with a remainder of 7 inches. Result: 2' 7".

Multiplying a length by a number gives a longer (or shorter) length. Dividing a length by a number gives equal parts, still a length. Multiplying a length by a length gives an area in square feet or square inches. Dividing a length by a length gives a plain count: how many times the second fits into the first.

Multiply 3' 4" by 2

Convert to total inches: 3' 4" = 36 + 4 = 40 inches. Multiply: 40 × 2 = 80 inches. Convert back: 80 ÷ 12 = 6 feet with a remainder of 8 inches. Result: 6' 8".

Multiply Length × Length (Area)

A room 10' x 12' has an area of 120 square feet. The calculator converts to total inches: 120" × 144" = 17,280 square inches. Divide by 144 to get square feet: 120 sq ft. For metric, multiply square inches by 0.00064516 to get square meters.

Divide 6' 8" by 2

Convert to total inches: 6' 8" = 72 + 8 = 80 inches. Divide: 80 ÷ 2 = 40 inches. Convert back: 40 ÷ 12 = 3 feet with a remainder of 4 inches. Result: 3' 4".

Divide 8' by 1' 4"

Convert to total inches: 8' = 96 inches. 1' 4" = 16 inches. Divide: 96 ÷ 16 = 6. Result: 6 pieces fit.

Rounding to the nearest 1/16" is the standard for finish carpentry and trim work. The calculator splits the rounded length into feet and inches after rounding, so 5' 11.99" at 1/16" precision becomes 6' 0", never 5' 12" or 5' 11 1/1". This matters because a misrounded result on a cut list means a piece that does not fit. For rough framing, 1/8" precision is adequate. For precision work like cabinetmaking, use 1/32" or 1/64". The calculator supports all these: 1/2", 1/4", 1/8", 1/16", 1/32", and 1/64".

Add 5' 8" and 3' 7". Convert to total inches: 5' 8" = (5 × 12) + 8 = 60 + 8 = 68 inches. 3' 7" = (3 × 12) + 7 = 36 + 7 = 43 inches. Add: 68 + 43 = 111 inches. Convert back: 111 ÷ 12 = 9 feet with a remainder of 3 inches. Result: 9' 3".

Subtract 2' 8" from 5' 3". Convert to total inches: 5' 3" = 60 + 3 = 63 inches. 2' 8" = 24 + 8 = 32 inches. Subtract: 63 − 32 = 31 inches. Convert back: 31 ÷ 12 = 2 feet with a remainder of 7 inches. Result: 2' 7".

Multiply 3' 4" by 2. Convert to total inches: 3' 4" = 36 + 4 = 40 inches. Multiply: 40 × 2 = 80 inches. Convert back: 80 ÷ 12 = 6 feet with a remainder of 8 inches. Result: 6' 8".

Divide 6' 8" by 2. Convert to total inches: 6' 8" = 72 + 8 = 80 inches. Divide: 80 ÷ 2 = 40 inches. Convert back: 40 ÷ 12 = 3 feet with a remainder of 4 inches. Result: 3' 4".

Convert 45 inches to feet and inches. Divide 45 by 12: 45 ÷ 12 = 3 feet with a remainder of 9 inches. Result: 3' 9". The calculator does this for you in reverse when you enter a length in total inches.

A tape measure shows fractions: 1/2", 1/4", 1/8", 1/16". The calculator accepts these directly. Enter 7 3/8" and it parses correctly. This is the same input as reading a tape measure. The hook on a tape measure is designed with a sliding tang about 1/16" thick to compensate for inside and outside measurements. The calculator accounts for this by treating your entry as the actual length, not the tape reading.