Feet and Inch Calculator

Add, subtract, multiply, and divide feet, inches, and fractions for carpentry, construction, and DIY. Get instant decimal feet and metric conversions.

Feet & Inches Input

US Customary
Select Arithmetic Operation
Carpentry Presets
First Measurement (Value 1)
ft
in
Second Measurement (Value 2)
ft
in
Calculated Dimension
9′ 3″ (9 ft 3 in)
9.25 Decimal Feet

Total Inches

111″

Decimal Feet

9.25 ft

Centimeters

281.94 cm

Meters

2.819 m

Dimension Equivalent Conversions

Value 1 (5′ 6″)66″ (5.500 ft)167.6 cm
Value 2 (3′ 9″)45″ (3.750 ft)114.3 cm

Framing & Stud Layout Tip

Standard wall framing studs are placed 16 inches on center (1.333 decimal feet) or 24 inches on center (2.000 decimal feet), allowing standard 48″ × 96″ drywall panels to break cleanly over stud centers.

How to Perform Feet and Inches Arithmetic

Working with US Customary units on construction blueprints requires converting mixed feet and inches into a common baseline (total inches or decimal feet) before performing arithmetic, then converting back to standard tape-measure fractions.

1. Converting Feet & Inches to Total Baseline Inches
Total Inches=(Feet × 12) + Inches;Decimal Feet=Feet +
Inches12
2. Converting Total Inches Back to Feet & Inches
Feet=⌊Total Inches ÷ 12⌋;Remaining Inches=Total Inches modulo 12
Step-by-Step Calculation Breakdown
Step 1: Convert Both Inputs to Baseline Total Inches (5′ 6″ + 3′ 9″)
Measurement 1 = (5 × 12) + 6 = 66 inches (5.500 ft)
Measurement 2 = (3 × 12) + 9 = 45 inches (3.750 ft)
Step 2: Perform Operation (Addition)
Combined Total Inches = 66″ + 45″ = 111.00 inches
Step 3: Convert Back to Architectural Format & Metric
Result=111 ÷ 12 = 9 ft with 3 in remainder=9′ 3″ (9.25 ft / 281.94 cm / 2.819 m)

Inches & Fractions to Decimal Feet Conversion Table

Inches (Fraction / Whole)Decimal InchesDecimal FeetMillimeters (mm)
1/8″0.125″0.0104 ft3.175 mm
1/4″0.250″0.0208 ft6.350 mm
1/2″0.500″0.0417 ft12.700 mm
3/4″0.750″0.0625 ft19.050 mm
3″3.000″0.2500 ft76.200 mm
6″6.000″0.5000 ft152.400 mm
9″9.000″0.7500 ft228.600 mm

Frequently Asked Questions

How do I add feet and inches together?
To add feet and inches: convert each measurement into total inches (Feet × 12 + Inches), add the inches together, then divide by 12 to get whole feet with remaining inches. For example, 5′ 6″ (66″) + 3′ 9″ (45″) = 111″ total, which equals 9′ 3″ (9.25 decimal feet).
How do I convert inches to decimal feet?
Divide the number of inches by 12 and add the result to whole feet. For example, 9 inches is 9 ÷ 12 = 0.75 feet. Therefore, 6 feet 9 inches is equal to 6.75 decimal feet. Decimal feet are required when calculating area (sq ft) or volume (cu yds).
How do I divide a board length into equal sections?
Convert the total length to inches, divide by the number of desired segments, and convert back to feet, inches, and sixteenths. For example, dividing a 10′ 6″ board (126″) into 3 equal pieces yields 126 ÷ 3 = 42″ (3′ 6″) per segment.
What is the difference between architectural feet-inches and engineering decimal feet?
Architects and carpenters write dimensions in fractional feet and inches (e.g. 14′ 6-1/2″) to match standard tape measures. Civil engineers and land surveyors use decimal feet (e.g. 14.54 ft) subdivided into tenths and hundredths of a foot.

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