Deck Material Calculator
Estimate decking boards, joists, posts, concrete, screws, and cost from deck length and width. Free deck material calculator for DIY builds.
How to use this deck material calculator
A deck material calculator turns a rectangle into a shopping list: decking, joists, rim joists, posts, footings, and fasteners. Defaults match common pressure-treated 5/4×6 decking (about 5½″ actual width) with a ⅛″ gap and 16″ joist spacing. Change board width for 2×6 or composite planks.
Framing here is a typical single-span deck with beams along the length and joists across the width. Always follow local code, span tables, and your lumber grade—this is a materials estimate, not an engineered plan. Add extra boards if you picture-frame the perimeter or run boards at 45°.
Formula
Worked example
A 16×12 ft deck with 5.5″ boards, ⅛″ gaps, 16 ft boards, and 10% waste needs about 29 decking boards, 13 joists at 16″ OC, and roughly 6 posts.
Related calculators
More home calculators
- Paint Calculator — Calculate how much paint you need from wall size, doors, windows, and coats. Get paintable area, gallons, liters, and how many cans to buy.
- Concrete Calculator — Calculate cubic yards of concrete for slabs, footings, columns, walls, and circular pads. Includes cubic feet, cubic meters, bags, waste, and optional cost.
- Gravel Calculator — Estimate gravel cubic yards and tons from length, width, depth, and rock type. Optional cost per ton for driveways, pads, and paths.
- Flooring Calculator — Add up to four rooms, then calculate flooring square footage, extra material for waste, boxes if you know coverage per box, and optional cost.
- Tile Calculator — Calculate how many tiles you need from room size, tile width and height, grout spacing, and waste. Optional tiles per box and material cost.
- Drywall Calculator — Estimate drywall sheets from room length, width, and height. Subtract doors and windows, add a ceiling, and choose 4×8, 4×10, or 4×12 ft sheets.
Frequently asked questions
How many decking boards do I need?
Divide the deck width by the laid width of one board (board + gap), then multiply by how many board lengths fit the run, and add waste. This tool does that math.
How much waste should I add?
10% is a solid default for straight runs. Use 12–15% for diagonal decking, picture frames, or lots of cuts.
16″ or 24″ joist spacing?
16″ on center is the usual residential choice, especially under composite. 24″ is only for lumber and spans the joist tables allow.
How many concrete bags per footing?
About two to three 80 lb bags per 12″-class footing, more for frost-depth tubes. This estimate uses three bags each.
Does this include railing and stairs?
No. Add posts, balusters, and stair stringers separately. The square footage of the walking surface is the starting point.
How many deck boards do I need?
Divide deck width by the laid width of one board (board + gap), multiply by lengths along the run, and add waste. This tool does that math.
Does this include railing?
No. Add posts, balusters, and stairs separately. The walking surface is the starting point.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-20.