Foot and Inch Calculator

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How to Use the Foot and Inch Calculator

Whether you are a carpenter, a home DIY enthusiast, or an architect, working with the Imperial system can be challenging when you need to add or subtract measurements. Our Foot and Inch Calculator simplifies this process by handling the base-12 conversion for you automatically.

Common Calculation Scenarios

In many construction projects, you aren't just dealing with whole numbers. You might need to add a 5′ 8″ board to a 3′ 10″ board. While you could convert everything to inches, calculate, and convert back, this tool does it in one click.

• Room Dimensions: Adding closet space to bedroom length.
• Woodworking: Calculating total lumber length required for a project.
• Height Differences: Calculating the difference in height between two people or objects.

Example Calculations

Let's look at how the math works behind the scenes:

Example 1 (Addition): 5′ 10″ + 2′ 6″

1. Total the inches: 10 + 6 = 16 inches.
2. Convert inches to feet: 16 inches = 1 foot and 4 inches.
3. Total the feet: 5 + 2 + 1 (carried over) = 8 feet.
4. Result: 8′ 4″

Example 2 (Subtraction): 10′ 2″ – 4′ 8″

1. Since 2 is less than 8, borrow 1 foot (12 inches) from the 10 feet.
2. New values: 9′ 14″ – 4′ 8″.
3. Subtract inches: 14 – 8 = 6 inches.
4. Subtract feet: 9 – 4 = 5 feet.
5. Result: 5′ 6″

Why Base-12 Matters

The primary reason measurement calculations are difficult is that the Imperial system is not decimal-based. While the standard number system is base-10, feet and inches are base-12. This means standard calculators cannot be used for measurements without converting them to decimals first. Using this specialized tool prevents errors that occur when people accidentally treat 10 inches as 0.10 feet.

function calculateFootInches() { var f1 = parseFloat(document.getElementById('feet1').value) || 0; var i1 = parseFloat(document.getElementById('inches1').value) || 0; var f2 = parseFloat(document.getElementById('feet2').value) || 0; var i2 = parseFloat(document.getElementById('inches2').value) || 0; var op = document.getElementById('operation').value; // Convert everything to total inches var totalInches1 = (f1 * 12) + i1; var totalInches2 = (f2 * 12) + i2; var finalTotalInches = 0; if (op === 'add') { finalTotalInches = totalInches1 + totalInches2; } else { finalTotalInches = totalInches1 – totalInches2; } var isNegative = finalTotalInches < 0; var absInches = Math.abs(finalTotalInches); var resultFeet = Math.floor(absInches / 12); var resultInches = (absInches % 12).toFixed(2); // Clean up trailing zeros on inches if possible if (resultInches.endsWith('.00')) { resultInches = Math.floor(resultInches); } var resultDisplay = document.getElementById('mainResult'); var decimalDisplay = document.getElementById('decimalResult'); var resultArea = document.getElementById('resultArea'); var sign = isNegative ? "-" : ""; resultDisplay.innerHTML = sign + resultFeet + "' " + resultInches + '"'; var decimalFeet = (finalTotalInches / 12).toFixed(3); decimalDisplay.innerHTML = "Total in Decimal Feet: " + decimalFeet + " ft | Total Inches: " + finalTotalInches.toFixed(2) + " in"; resultArea.style.display = 'block'; }