Inches to Feet and Inches: Reading 5′10″ and Decimal Feet

1 ft = 12 in exactly. To write a length in feet and inches:

1. Divide the inches by 12. The whole number is the feet.
2. The remainder is the inches.

70 in: 70 ÷ 12 = 5 remainder 10 → 5 ft 10 in. 100 in: 100 ÷ 12 = 8 remainder 4 → 8 ft 4 in.

The reverse: feet × 12 + inches. 6 ft 2 in = 72 + 2 = 74 in.

A decimal foot is a fraction of 12 inches, not of 10. To convert the decimal part, multiply it by 12:

• 5.5 ft = 5 ft + 0.5 × 12 in = 5 ft 6 in (not 5 ft 5 in).
• 5.25 ft = 5 ft 3 in.
• 5.83 ft ≈ 5 ft 10 in (0.83 × 12 ≈ 10).
• 5.10 ft = 5 ft 1.2 in — not 5 ft 10 in.

Going the other way, 5 ft 10 in = 5 + 10/12 = 5.83 ft. Writing it as "5.10 ft" is wrong by almost 9 inches.

• ′ (prime) means feet; ″ (double prime) means inches. 5′10″ = 5 ft 10 in. Straight quote marks (5'10") are a common keyboard substitute.
• ft and in are the abbreviations; "ft." and "in." with a full stop also appear.
• Fractions of an inch are usually halves, quarters, eighths or sixteenths: 2′ 3½″ = 27.5 in.
• Dimensions such as 6′ × 8′ give two lengths, normally width × length; the source should say which is which.

Carry over every 12 inches, as you would carry every 10 in ordinary addition.

3 ft 8 in + 2 ft 7 in = 5 ft 15 in = 6 ft 3 in.

For subtraction, borrow 12 inches from the feet: 6 ft 2 in − 1 ft 9 in = 5 ft 14 in − 1 ft 9 in = 4 ft 5 in. Converting both to inches first (74 − 21 = 53 in = 4 ft 5 in) avoids the borrowing.

Convert to total inches first, then multiply by 2.54 (exact): 5 ft 10 in = 70 in × 2.54 = 177.8 cm. Do not multiply "5.10" by 30.48 — that treats it as decimal feet and gives 155.4 cm. Use the inches to centimetres converter for the final step.

• Treating the decimal part of feet as inches (5.5 ft ≠ 5 ft 5 in).
• Writing feet-and-inches with a decimal point (5.10 for 5′10″).
• Forgetting to carry when inches reach 12.
• Confusing ′ and ″.
• Converting feet and inches to metric separately and adding the rounded results.

• Inches to feet converter for decimal-feet arithmetic, and feet to metres.
• How inches and feet fit into Imperial and US customary units: Metric vs Imperial guide.

Definitions are listed on the methodology page.