📏 Feet and Inches Calculator
Convert, Add, Subtract, and Calculate Measurements with Precision
Measurement Calculator
Convert to Inches/Centimeters
Add Two Measurements
Subtract Two Measurements
Multiply by a Number
Divide by a Number
Results:
Understanding Feet and Inches Measurements
The feet and inches system is part of the imperial measurement system, widely used in the United States and a few other countries. Understanding how to work with feet and inches is essential for construction, interior design, carpentry, and everyday measurements.
Basic Conversions
The fundamental relationship between feet and inches is straightforward:
- 1 foot = 12 inches
- 1 inch = 2.54 centimeters
- 1 foot = 30.48 centimeters
- 1 foot = 0.3048 meters
Converting Feet and Inches to Total Inches
To convert a measurement expressed in feet and inches to total inches, use this formula:
Total Inches = (Feet × 12) + Inches
Example: 5 feet 9 inches
Total Inches = (5 × 12) + 9 = 60 + 9 = 69 inches
Example: 5 feet 9 inches
Total Inches = (5 × 12) + 9 = 60 + 9 = 69 inches
Converting Total Inches to Feet and Inches
To convert total inches back to feet and inches:
Feet = Total Inches ÷ 12 (whole number)
Remaining Inches = Total Inches mod 12
Example: 69 inches
Feet = 69 ÷ 12 = 5 feet (with remainder)
Remaining Inches = 69 – (5 × 12) = 9 inches
Result: 5 feet 9 inches
Remaining Inches = Total Inches mod 12
Example: 69 inches
Feet = 69 ÷ 12 = 5 feet (with remainder)
Remaining Inches = 69 – (5 × 12) = 9 inches
Result: 5 feet 9 inches
Converting to Metric System
Converting feet and inches to centimeters or meters is common in international contexts:
Centimeters = (Feet × 30.48) + (Inches × 2.54)
Example: 5 feet 9 inches to centimeters
Centimeters = (5 × 30.48) + (9 × 2.54)
Centimeters = 152.4 + 22.86 = 175.26 cm
Example: 5 feet 9 inches to centimeters
Centimeters = (5 × 30.48) + (9 × 2.54)
Centimeters = 152.4 + 22.86 = 175.26 cm
Adding Feet and Inches
When adding measurements in feet and inches, follow these steps:
- Add the feet together
- Add the inches together
- If inches total 12 or more, convert to additional feet
Example: Add 5 feet 9 inches + 3 feet 6 inches
Feet: 5 + 3 = 8 feet
Inches: 9 + 6 = 15 inches
Since 15 inches = 1 foot 3 inches
Final Result: 8 + 1 = 9 feet 3 inches
Feet: 5 + 3 = 8 feet
Inches: 9 + 6 = 15 inches
Since 15 inches = 1 foot 3 inches
Final Result: 8 + 1 = 9 feet 3 inches
Subtracting Feet and Inches
Subtraction requires careful attention to borrowing when necessary:
- Subtract the inches first
- If the result is negative, borrow 12 inches (1 foot) from the feet
- Subtract the feet
Example: Subtract 3 feet 9 inches from 7 feet 2 inches
Inches: 2 – 9 = -7 (need to borrow)
Borrow 1 foot: 7 feet becomes 6 feet, 2 inches becomes 14 inches
Inches: 14 – 9 = 5 inches
Feet: 6 – 3 = 3 feet
Final Result: 3 feet 5 inches
Inches: 2 – 9 = -7 (need to borrow)
Borrow 1 foot: 7 feet becomes 6 feet, 2 inches becomes 14 inches
Inches: 14 – 9 = 5 inches
Feet: 6 – 3 = 3 feet
Final Result: 3 feet 5 inches
Multiplying Feet and Inches
To multiply a measurement by a whole number or decimal:
- Convert the measurement to total inches
- Multiply by the number
- Convert back to feet and inches
Example: Multiply 4 feet 6 inches by 3
Total inches: (4 × 12) + 6 = 54 inches
Multiply: 54 × 3 = 162 inches
Convert: 162 ÷ 12 = 13 feet 6 inches
Result: 13 feet 6 inches
Total inches: (4 × 12) + 6 = 54 inches
Multiply: 54 × 3 = 162 inches
Convert: 162 ÷ 12 = 13 feet 6 inches
Result: 13 feet 6 inches
Dividing Feet and Inches
Division follows a similar process:
- Convert to total inches
- Divide by the number
- Convert the result back to feet and inches
Example: Divide 10 feet 8 inches by 2
Total inches: (10 × 12) + 8 = 128 inches
Divide: 128 ÷ 2 = 64 inches
Convert: 64 ÷ 12 = 5 feet 4 inches
Result: 5 feet 4 inches
Total inches: (10 × 12) + 8 = 128 inches
Divide: 128 ÷ 2 = 64 inches
Convert: 64 ÷ 12 = 5 feet 4 inches
Result: 5 feet 4 inches
Practical Applications
Construction and Carpentry
In construction, precise measurements in feet and inches are critical for:
- Cutting lumber to exact lengths
- Measuring room dimensions for flooring and wall materials
- Calculating material quantities (drywall, siding, roofing)
- Determining ceiling heights and door frame sizes
Interior Design
Designers use feet and inches measurements for:
- Furniture placement and spatial planning
- Window treatment measurements
- Determining appropriate furniture sizes for rooms
- Creating scaled floor plans
Height Measurements
Human height is commonly expressed in feet and inches in the United States. Average heights:
- Adult male: approximately 5 feet 9 inches (175 cm)
- Adult female: approximately 5 feet 4 inches (163 cm)
- Doorway standard: 6 feet 8 inches (80 inches)
- Ceiling standard: 8 feet (96 inches)
Common Fractional Inches
In practical use, inches are often divided into fractions rather than decimals:
- 1/2 inch = 0.5 inches
- 1/4 inch = 0.25 inches
- 1/8 inch = 0.125 inches
- 1/16 inch = 0.0625 inches
- 3/4 inch = 0.75 inches
- 3/8 inch = 0.375 inches
Tips for Accurate Measurements
- Use quality measuring tools: A reliable tape measure or ruler is essential
- Measure twice: Always verify measurements before cutting or ordering materials
- Account for fractions: Be precise with fractional inches for professional results
- Know your conversions: Keep conversion factors handy when working with metric
- Mark clearly: Use clear markings when transferring measurements
- Consider tolerances: Some applications require exact measurements, others allow slight variance
Common Measurement Mistakes to Avoid
- Forgetting to convert: Always ensure all measurements are in the same unit system
- Rounding too early: Keep full precision until the final calculation
- Misreading fractions: 3/8 inch is not the same as 0.38 inches (it's 0.375)
- Not accounting for material thickness: Remember to add or subtract material width
- Ignoring the starting point: Ensure your tape measure starts at true zero
Standard Building Dimensions
Familiarize yourself with these common construction measurements:
- Stud spacing: 16 inches on center (standard wall framing)
- Door width: 2 feet 8 inches to 3 feet (32-36 inches)
- Window sill height: 3 feet to 3 feet 6 inches from floor
- Counter height: 3 feet (36 inches)
- Bar height: 3 feet 6 inches (42 inches)
- Handrail height: 2 feet 10 inches to 3 feet 2 inches (34-38 inches)
Working with Large Measurements
For larger projects, understanding how to handle extensive measurements is crucial:
Example: A room measuring 15 feet 7 inches by 12 feet 9 inches
Convert to inches for area calculation:
Length: (15 × 12) + 7 = 187 inches
Width: (12 × 12) + 9 = 153 inches
Area in square inches: 187 × 153 = 28,611 square inches
Convert to square feet: 28,611 ÷ 144 = 198.7 square feet
Convert to inches for area calculation:
Length: (15 × 12) + 7 = 187 inches
Width: (12 × 12) + 9 = 153 inches
Area in square inches: 187 × 153 = 28,611 square inches
Convert to square feet: 28,611 ÷ 144 = 198.7 square feet
Conclusion
Mastering feet and inches calculations is an invaluable skill for anyone working in construction, design, or home improvement. Whether you're measuring for new furniture, planning a renovation, or building from scratch, understanding these conversions and calculations ensures accuracy and professional results. Use this calculator to quickly perform conversions and arithmetic operations, saving time and reducing errors in your projects.
Original Measurement: ' + feet + ' feet ' + inches + ' inches
';
html += 'Total Inches: ' + totalInches.toFixed(2) + ' inches
';
html += 'Centimeters: ' + totalCm.toFixed(2) + ' cm
';
html += 'Meters: ' + totalMeters.toFixed(4) + ' m
';
} else if (calcType === "add") {
var feet1 = parseFloat(document.getElementById("feet2a").value);
var inches1 = parseFloat(document.getElementById("inches2a").value);
var feet2 = parseFloat(document.getElementById("feet2b").value);
var inches2 = parseFloat(document.getElementById("inches2b").value);
if (isNaN(feet1)) feet1 = 0;
if (isNaN(inches1)) inches1 = 0;
if (isNaN(feet2)) feet2 = 0;
if (isNaN(inches2)) inches2 = 0;
var totalFeet = feet1 + feet2;
var totalInches = inches1 + inches2;
while (totalInches >= 12) {
totalFeet += 1;
totalInches -= 12;
}
var allInches = (totalFeet * 12) + totalInches;
html += 'First Measurement: ' + feet1 + ' feet ' + inches1 + ' inches
';
html += 'Second Measurement: ' + feet2 + ' feet ' + inches2 + ' inches
';
html += 'Sum: ' + totalFeet + ' feet ' + totalInches.toFixed(2) + ' inches
';
html += 'Total Inches: ' + allInches.toFixed(2) + ' inches
';
} else if (calcType === "subtract") {
var feet1 = parseFloat(document.getElementById("feet2a").value);
var inches1 = parseFloat(document.getElementById("inches2a").value);
var feet2 = parseFloat(document.getElementById("feet2b").value);
var inches2 = parseFloat(document.getElementById("inches2b").value);
if (isNaN(feet1)) feet1 = 0;
if (isNaN(inches1)) inches1 = 0;
if (isNaN(feet2)) feet2 = 0;
if (isNaN(inches2)) inches2 = 0;
var totalInches1 = (feet1 * 12) + inches1;
var totalInches2 = (feet2 * 12) + inches2;
var diffInches = totalInches1 – totalInches2;
var resultFeet = Math.floor(Math.abs(diffInches) / 12);
var resultInches = Math.abs(diffInches) % 12;
if (diffInches 0) {
resultInches = -resultInches;
}
}
html += 'First Measurement: ' + feet1 + ' feet ' + inches1 + ' inches
';
html += 'Second Measurement: ' + feet2 + ' feet ' + inches2 + ' inches
';
html += 'Difference: ' + resultFeet + ' feet ' + resultInches.toFixed(2) + ' inches
';
html += 'Difference in Inches: ' + diffInches.toFixed(2) + ' inches
';
} else if (calcType === "multiply") {
var feet = parseFloat(document.getElementById("feet3").value);
var inches = parseFloat(document.getElementById("inches3").value);
var multiplier = parseFloat(document.getElementById("multiplier").value);
if (isNaN(feet)) feet = 0;
if (isNaN(inches)) inches = 0;
if (isNaN(multiplier)) multiplier = 1;
var totalInches = (feet * 12) + inches;
var resultInches = totalInches * multiplier;
var resultFeet = Math.floor(resultInches / 12);
var remainingInches = resultInches % 12;
html += 'Original Measurement: ' + feet + ' feet ' + inches + ' inches
';
html += 'Multiplied By: ' + multiplier + '
';
html += 'Result: ' + resultFeet + ' feet ' + remainingInches.toFixed(2) + ' inches
';
html += 'Total Inches: ' + resultInches.toFixed(2) + ' inches
';
} else if (calcType === "divide") {
var feet = parseFloat(document.getElementById("feet3").value);
var inches = parseFloat(document.getElementById("inches3").value);
var divisor = parseFloat(document.getElementById("multiplier").value);
if (isNaN(feet)) feet = 0;
if (isNaN(inches)) inches = 0;
if (isNaN(divisor) || divisor === 0) {
resultContent.innerHTML = 'Error: Cannot divide by zero
';
resultDiv.style.display = "block";
return;
}
var totalInches = (feet * 12) + inches;
var resultInches = totalInches / divisor;
var resultFeet = Math.floor(resultInches / 12);
var remainingInches = resultInches % 12;
html += 'Original Measurement: ' + feet + ' feet ' + inches + ' inches
';
html += 'Divided By: ' + divisor + '
';
html += 'Result: ' + resultFeet + ' feet ' + remainingInches.toFixed(2) + ' inches
';
html += 'Total Inches: ' + resultInches.toFixed(2) + ' inches
';
}
resultContent.innerHTML = html;
resultDiv.style.display = "block";
}
toggleCalculationType();