📐 Feet and Inches Calculator
Add, subtract, multiply, and divide imperial measurements with ease — perfect for construction, carpentry, and DIY projects in 2026
📑 Table of Contents
📊 Understanding Feet and Inches Calculations
The feet and inches calculator is an essential 2026 tool for anyone working with imperial measurements in construction, carpentry, or DIY projects. Unlike standard calculators, this specialized tool handles the complexity of the imperial system where 12 inches equal 1 foot, automatically managing conversions and fractional inches (1/16" to 15/16") that are standard in building trades.
Whether you're a contractor calculating lumber lengths, a carpenter planning furniture dimensions, or a homeowner measuring for renovations, this calculator eliminates manual conversion errors and provides instant, accurate results in both feet-inches and decimal formats.
Key benefit: Perform complex imperial math operations in seconds with professional precision up to 1/16 inch — saving time and preventing costly measurement mistakes.
⚡ Feet and Inches Calculator
📏 First Measurement
📏 Second Measurement / Multiplier
For multiply/divide: Enter number in Feet field (e.g., 3 to multiply by 3)
📋 Quick Reference:
12 inches = 1 foot
3 feet = 1 yard
1 foot = 30.48 cm
1 inch = 2.54 cm
📝 How to Use the Feet and Inches Calculator
Our feet and inches calculator simplifies complex imperial measurements by handling all conversions automatically. Follow these steps:
- Enter your first measurement — Input feet in the first field, whole inches in the second, and select any fractional inches (1/16" to 15/16") from the dropdown. For example, 5' 7-1/2" would be: Feet=5, Inches=7, Fraction=1/2".
- Select your operation — Choose Addition (+), Subtraction (−), Multiplication (×), Division (÷), or Convert to Decimal. The calculator adapts to show appropriate input fields.
- Enter second measurement or multiplier — For add/subtract, enter another measurement. For multiply/divide, enter the number in the Feet field (e.g., "3" to multiply by 3).
- Click "Calculate Result" — Get instant results in both feet-inches format and decimal feet, perfect for different applications.
- Use the decimal output — The decimal result is ideal for CAD software, CNC machines, or cross-referencing with metric measurements.
💡 Avoid Common Mistakes: When entering inches, only use 0-11 (not 12+). Extra inches automatically convert to feet. Always verify fractions — 1/4" and 1/2" are the most commonly confused!
📐 Feet and Inches Formulas & Calculation Methods
Understanding these formulas ensures you can verify calculations and work confidently with imperial measurements:
Convert Feet-Inches to Total Inches
This is the foundation of all calculations. Convert everything to inches first, perform the math, then convert back.
Example: 5' 7-1/2" = (5 × 12) + 7 + 0.5 = 67.5 inches
Convert Total Inches Back to Feet-Inches
Remaining Inches = Total Inches mod 12
The "floor" function rounds down to the nearest whole number. The "mod" function gives the remainder after division.
Example: 85 inches = floor(85÷12) = 7 feet, remainder 85 mod 12 = 1 inch → 7' 1"
Addition Formula
Add feet and inches separately, then normalize if inches ≥ 12 by converting excess to feet.
Example: 4' 9" + 2' 7" = 6' 16" → 7' 4" (since 16" = 1' 4")
Decimal Feet Conversion
Useful for CAD software, spreadsheets, and metric conversions.
Example: 3' 6" = 3 + (6÷12) = 3.5 feet
📊 Feet and Inches Examples
Example 1: Adding Board Lengths (Construction)
Scenario: Mike the carpenter is joining two boards for a deck rail. Board 1 is 8' 3-1/4" and Board 2 is 6' 9-3/4".
Input Values:
- First Measurement: 8 feet, 3 inches, 1/4" fraction
- Operation: Addition
- Second Measurement: 6 feet, 9 inches, 3/4" fraction
Calculation:
- Convert to inches: 8' 3-1/4" = 99.25" and 6' 9-3/4" = 81.75"
- Add: 99.25 + 81.75 = 181 inches
- Convert back: 181 ÷ 12 = 15' 1"
Result: 15 feet 1 inch (15.083 decimal feet)
Example 2: Cutting Material from Stock (Woodworking)
Scenario: Sarah has a 10-foot board and needs to cut off 3' 7-1/2" for a shelf. How much remains?
Input Values:
- First Measurement: 10 feet, 0 inches, 0 fraction
- Operation: Subtraction
- Second Measurement: 3 feet, 7 inches, 1/2" fraction
Calculation:
- 10' 0" = 120 inches
- 3' 7-1/2" = 43.5 inches
- Subtract: 120 - 43.5 = 76.5 inches
- Convert: 76.5 ÷ 12 = 6' 4-1/2"
Result: 6 feet 4-1/2 inches remaining (6.375 decimal feet)
Example 3: Calculating Total Length for Multiple Pieces (DIY)
Scenario: James needs 8 identical fence pickets, each 3' 6" tall. What's the total lumber needed?
Input Values:
- First Measurement: 3 feet, 6 inches, 0 fraction
- Operation: Multiplication
- Second Measurement: 8 (in Feet field)
Calculation:
- 3' 6" = 42 inches
- Multiply: 42 × 8 = 336 inches
- Convert: 336 ÷ 12 = 28 feet
Result: 28 feet 0 inches total lumber needed (28.0 decimal feet)
📊 Imperial Measurement Reference Tables 2026
Fraction to Decimal Conversion
| Fraction | Decimal (inches) | Millimeters |
|---|---|---|
| 1/16" | 0.0625 | 1.59 mm |
| 1/8" | 0.125 | 3.18 mm |
| 3/16" | 0.1875 | 4.76 mm |
| 1/4" | 0.25 | 6.35 mm |
| 5/16" | 0.3125 | 7.94 mm |
| 3/8" | 0.375 | 9.53 mm |
| 7/16" | 0.4375 | 11.11 mm |
| 1/2" | 0.5 | 12.70 mm |
| 9/16" | 0.5625 | 14.29 mm |
| 5/8" | 0.625 | 15.88 mm |
| 11/16" | 0.6875 | 17.46 mm |
| 3/4" | 0.75 | 19.05 mm |
| 13/16" | 0.8125 | 20.64 mm |
| 7/8" | 0.875 | 22.23 mm |
| 15/16" | 0.9375 | 23.81 mm |
Common Length Conversions
| Imperial | Feet | Inches | Metric |
|---|---|---|---|
| 1 inch | 0.0833 ft | 1 in | 2.54 cm |
| 1 foot | 1 ft | 12 in | 30.48 cm |
| 1 yard | 3 ft | 36 in | 91.44 cm |
| 1 meter | 3.281 ft | 39.37 in | 100 cm |
| 8 feet (lumber) | 8 ft | 96 in | 243.84 cm |
| 10 feet (lumber) | 10 ft | 120 in | 304.8 cm |
| 12 feet (lumber) | 12 ft | 144 in | 365.76 cm |
Source: NIST Handbook 44 — Specifications and Tolerances for Reference Standards
💡 Important Tips for Feet and Inches Calculations
- Measure twice, cut once: Always verify your calculations before cutting materials. Use this calculator to double-check mental math.
- Account for kerf: When cutting multiple pieces from stock, remember that each saw cut removes material (typically 1/8" for circular saws).
- Nominal vs. actual lumber sizes: A 2×4 actually measures 1-1/2" × 3-1/2". Always use actual dimensions for precise calculations.
- Use decimal output for CAD: When inputting measurements into design software, use the decimal feet result for maximum accuracy.
- Round fractions consistently: When working with 1/16" precision, always round to the nearest 1/16" in the same direction throughout a project.
- Keep a conversion chart handy: Post the fraction-to-decimal table at your workstation for quick reference during projects.
🔧 Practical Applications
🏗️ Construction
Framing walls, calculating stud spacing, roofing measurements, foundation layouts.
🪚 Carpentry
Cabinet dimensions, trim work, furniture building, joint calculations.
🏠 Home DIY
Deck building, fence installation, flooring, shelving projects.
📐 Interior Design
Room layouts, furniture placement, window treatments, space planning.
❓ Frequently Asked Questions
There are exactly 12 inches in one foot. This relationship comes from historical measurement standards dating back to ancient civilizations. To convert feet to inches, multiply by 12; to convert inches to feet, divide by 12.
Add feet, inches, and fractions separately, then normalize the result. If fractions exceed 1 inch, convert to inches. If total inches exceed 12, convert to feet. Example: 3' 8-1/2" + 2' 6-3/4" = 5' 14-1/4" = 5' + 1' 2-1/4" = 6' 2-1/4".
5.5 feet equals 5 feet 6 inches. To convert, keep the whole number (5) as feet, then multiply the decimal (0.5) by 12 to get inches: 0.5 × 12 = 6 inches. This conversion is common when working with architectural plans.
The 12-inch foot originated from ancient Roman measuring systems. Twelve was favored because it's easily divisible by 2, 3, 4, and 6, making fractions simpler for trade and construction. This standard was formalized in 1959 when the international inch was defined as exactly 25.4 millimeters.
Nominal dimensions are the traditional names (like 2×4), while actual dimensions are the real measurements after drying and planing. A nominal 2×4 is actually 1-1/2" × 3-1/2". A 2×6 is actually 1-1/2" × 5-1/2". Always use actual dimensions for accurate project calculations.
Accuracy requirements vary by application: rough framing allows ±1/4 inch tolerance, finish carpentry requires ±1/16 inch, and precision cabinetry demands ±1/32 inch or better. Always follow building codes and project specifications for your specific application.
First convert to total inches, then multiply by 2.54 to get centimeters. Example: 5' 8" = 68 inches × 2.54 = 172.72 cm. Alternatively, use the decimal feet output and multiply by 30.48 to get centimeters directly.
A board foot measures lumber volume: (Thickness" × Width" × Length') ÷ 12. For example, a 2" × 6" × 10' board contains (2 × 6 × 10) ÷ 12 = 10 board feet. This calculation determines lumber costs at lumber yards.
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About the Author
Adam
Construction & Measurement Calculator Specialist
Adam specializes in developing practical calculation tools for construction professionals, carpenters, engineers, and DIY enthusiasts. With extensive experience in imperial measurement systems and building trades, Adam creates user-friendly calculators that solve real-world measurement challenges.
Disclaimer: This calculator is for educational and planning purposes. Always verify measurements before cutting materials. For structural calculations, consult a licensed engineer. Last updated: February 2026.
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