How board quantities are calculated
Inputs: length L and width W in feet; board face width b and gap g in inches; stock length s in feet; allowance r as a percentage. The board run is L when the board direction is “along length”, otherwise W. The dimension across the boards is the other dimension.
Number of courses = ceiling((12 × across + gap) ÷ (b + gap)). This computes enough whole-width courses to cover the input footprint; in real construction the outermost board may need ripping.
Pieces per course = ceiling(run ÷ stock length). Base pieces = courses × pieces per course. Purchase pieces = ceiling(base pieces × (1 + allowance ÷ 100)). Decking subtotal = purchase pieces × user-entered board unit price.
Important limitations
- Counts are conservative, not an optimized cutting or staggered-joint plan. Offcuts are not reused across courses.
- Only straight, rectangular, parallel-course layouts are supported. Diagonal installation, picture frames, herringbone, curved edges and stairs require a different takeoff.
- End joints, minimum supported bearing, span limits and proper fastening must be confirmed with product instructions and an appropriately designed frame.
- Allowance is applied to full stock-board count; it is not a guaranteed waste rate.
- Prices must be supplied by the user. Blank prices produce no dollar estimate. No automatic taxes, freight or installation charges are included.
- Board-count estimates are not structural engineering, a bill of materials for the entire deck, code advice or permit approval.
Reference material
For guidance on deck construction and relevant structural design limits, consult the American Wood Council's DCA 6 Residential Wood Deck Construction Guide. For applicable local requirements, contact your building department. Confirm product-specific spacing and fasteners with your chosen manufacturer. This reference does not certify the DeckWise estimates.
Version history
V1.0 · October 30, 2026: initial board estimate, length comparisons by changing stock selection, custom pricing, copy/print, mobile layout and explicit scope disclaimers. No verified retailer price feed.