Calculate Lumber

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Board Foot Lumber Calculator

Calculation Summary:

Total Board Feet: 0 BF

Total Cost Estimate: $0.00

function calculateLumber() { var thick = parseFloat(document.getElementById('thickness').value); var width = parseFloat(document.getElementById('width').value); var len = parseFloat(document.getElementById('length').value); var qty = parseFloat(document.getElementById('quantity').value); var price = parseFloat(document.getElementById('unitPrice').value) || 0; if (isNaN(thick) || isNaN(width) || isNaN(len) || isNaN(qty) || thick <= 0 || width <= 0 || len <= 0 || qty <= 0) { alert("Please enter valid positive numbers for all dimensions."); return; } // Formula: (Thickness in inches * Width in inches * Length in feet) / 12 var singleBoardFeet = (thick * width * len) / 12; var totalBoardFeet = singleBoardFeet * qty; var finalCost = totalBoardFeet * price; document.getElementById('totalBF').innerText = totalBoardFeet.toFixed(2); document.getElementById('totalCost').innerText = '$' + finalCost.toFixed(2); document.getElementById('lumber-results').style.display = 'block'; }

How to Calculate Board Feet for Your Project

Whether you are a professional woodworker or a DIY enthusiast, understanding how to calculate lumber is essential for accurate budgeting and material ordering. Hardwood is typically sold by the board foot (BF), which is a unit of volume.

What is a Board Foot?

A board foot is defined as a piece of lumber that is 12 inches wide, 12 inches long, and 1 inch thick. This equals 144 cubic inches. When purchasing hardwood, you are paying for the volume of the wood rather than the linear length.

The Board Foot Formula

To calculate the board footage of a piece of lumber, use the following standard formula:

(Thickness" × Width" × Length') / 12 = Board Feet

Note that the Length is measured in feet, while Thickness and Width are measured in inches. If your length is in inches, you must divide the total by 144 instead of 12.

Example Calculation

Suppose you are buying a board that is 2 inches thick, 6 inches wide, and 8 feet long:

  • Multiply Thickness (2) × Width (6) × Length (8) = 96
  • Divide by 12: 96 / 12 = 8 Board Feet

Nominal vs. Actual Dimensions

In the lumber industry, there is a difference between "nominal" and "actual" size. Softwoods (like construction 2x4s) are usually sold by nominal size, meaning a 2×4 actually measures 1.5″ x 3.5″. However, hardwoods are often sold in "quarters" for thickness (e.g., 4/4 is 1 inch, 8/4 is 2 inches). Always use the actual dimensions when calculating the specific volume needed for a precision project, but check with your lumber yard on how they bill for "surfaced" boards.

Tips for Buying Lumber

1. Add Waste: Always buy 15-20% more lumber than your calculation to account for knots, grain matching, and milling errors.
2. Check the Grade: Higher grades (FAS – First and Seconds) will have fewer defects but cost significantly more per board foot.
3. Verify Moisture Content: Ensure the lumber is kiln-dried (KD) if you are building indoor furniture to prevent warping.

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