How to use this calculator
Decking quantity is rows times pieces per row. Rows come from the actual board face width plus gap across the deck width; pieces per row come from the run divided by stock length. This simplified straight-layout method is honest about its limits: seams, offcuts and pattern layouts need a board-by-board plan.
Enter your own figures in the form above. A blank field is treated as missing — not as zero — so the tool will ask you to complete it. A genuine zero is accepted where it makes sense (for example, no HOA dues). Press Calculate for a breakdown, Load worked example to fill in the example below, or Reset to return to the defaults.
Formula and assumptions
Rows = (deck width in inches + gap) ÷ (board face width + gap), rounded UP. Pieces per row = run ÷ stock length, rounded UP (simplified straight layout). Purchase pieces = rows × pieces per row × (1 + waste %), rounded UP. Surface cost = purchase pieces × board price.
Worked example
Worked example: deck 12 ft wide × 16 ft run, 5.5 in face width, 0.25 in gap, 16 ft stock, no waste. Rows: (144 + 0.25) ÷ 5.75 = 25.09, rounded to 26 rows; pieces per row 1; purchase 26 full-length boards in this simplified layout.
Use the Load worked example button above to reproduce this example in the form, then change one input at a time to see what drives the result.
Limitations and common mistakes
No joist spacing, span, ledger, footing, railing or structural design is included. Diagonal layouts, picture framing, breaker boards and mixed stock lengths change the count and the offcut pattern; check seams against actual stock before ordering.
Frequently asked questions
Why actual face width, not nominal?
A nominal “6-inch” deck board is commonly 5.5 in actual face width. Using nominal width under-counts rows.
What if the run is longer than stock?
Each row then needs more than one piece plus a seam allowance. The tool rounds pieces per row up, but seam placement still needs a layout check.
Do gaps really matter?
Yes — across a wide deck, a quarter-inch gap per board accumulates to whole rows. Ignoring gaps under-counts.
Sources
No external price, product or market data is used on this page. Every price, density, coverage and rate is a figure you enter, or a clearly labelled illustrative default in the form. Check product labels and supplier quotes for the figures that apply to your job.
Estimates only. Results from this calculator are not a loan offer, appraisal, engineering design, equipment selection or contractor quote.