Deck Board Calculator
Estimate decking boards, rows and total purchased length.
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What this tool does
Estimate decking boards, rows and total purchased length. Boards run parallel to the entered length; joints are not stagger-optimized.
How to use the Deck Board Calculator
- Enter or select length in ft.
- Enter or select width in ft.
- Enter or select actual board width in in.
- Enter or select board gap in in.
- Enter or select board length in ft.
- Enter or select waste allowance (%).
- Read the calculated result; change any measurement to compare alternatives.
Formula
rows = ceil(width × 12 / (boardWidth + gap)); boards = ceil(rows × ceil(length / boardLength) × (1 + waste/100))
- length
- Length (ft, before metric conversion)
- width
- Width (ft, before metric conversion)
- boardWidth
- Actual board width (in, before metric conversion)
- gap
- Board gap (in, before metric conversion)
- boardLength
- Board length (ft, before metric conversion)
- waste
- Waste allowance (%)
Boards run parallel to the entered length; joints are not stagger-optimized.
Worked example
For deck board calculator, the following measurements illustrate the exact method: Length: 20; Width: 10; Actual board width: 5.5; Board gap: 0.125; Board length: 12; Waste allowance (%): 10.
Inputs
- Length20 ft
- Width10 ft
- Actual board width5.5 in
- Board gap0.125 in
- Board length12 ft
- Waste allowance (%)10
Result
- Boards to buy49
- Deck area200 sq ft
- Board rows22
- Linear feet purchased588 ft
Results explained
- Boards to buy
- Boards to buy from the formula above. Boards run parallel to the entered length; joints are not stagger-optimized.
- Deck area
- Deck area from the formula above, expressed in sqft before metric conversion. Boards run parallel to the entered length; joints are not stagger-optimized.
- Board rows
- Board rows from the formula above. Boards run parallel to the entered length; joints are not stagger-optimized.
- Linear feet purchased
- Linear feet purchased from the formula above, expressed in ft before metric conversion. Boards run parallel to the entered length; joints are not stagger-optimized.
Frequently asked questions
Round up rows by the actual board width plus gap, then round boards per row up to whole stock lengths.
Measure deck length, deck width, actual board width, gap and stock length.
Use 5–10% for simple layouts and 10–15% for diagonal cuts or complicated outlines; the allowance is editable.
Split the outline into rectangles or triangles and calculate each section separately. Do not count overlapping sections twice.
This is a purchasing estimate, not a structural design. Confirm measurements and local requirements before buying or building.