Feet-Inch-Fraction Calculator
Convert construction dimensions between feet-inches-fractions and metric, and round to a buildable increment.
Feet/inches/fractions, decimal, or metric (mm/cm/m). A bare number is inches.
Why a dedicated feet-inch calculator?
Most converters only accept decimals. Construction documents speak in
feet, inches, and fractions — like 12' 4-3/8" — and need
results rounded to the nearest 1/16" or 1/8". This tool parses that dialect
directly, converts cleanly to millimeters (the exact basis is 1 inch =
25.4 mm), and rounds the imperial result to the increment you choose.
Enter a value any way you like: 12' 4-3/8", 12.5',
148.375", 3810 mm, or a bare number (treated as
inches).
Frequently asked questions
How do I convert feet and inches to millimeters?
Multiply the feet by 304.8 and the inches by 25.4, then add them. For example, 12' 4-3/8" is 3771.9 mm. The conversion is exact by definition: 1 inch = 25.4 mm and 1 foot = 304.8 mm.
How do you add feet-inch-fraction dimensions?
Convert each dimension to a single unit (inches or millimeters), add them, then convert back and round to your chosen fraction such as 1/16". Carries are handled automatically, so 11-15/16" plus 1/16" rolls up to 12" (1'-0").
What is 1 inch in millimeters?
Exactly 25.4 mm — that is the definition of the inch, not a rounded value. One foot is exactly 304.8 mm (12 × 25.4).