Decking Calculator
How many deck boards and screws you need by deck size.
Doing this for work? Estimate the whole job in minutes.
JRIQ turns plans and site photos into full material + labor estimates with AI — built by the team behind these calculators.
Try it free →
Decking is the surface you walk on — the satisfying part that goes on fast once the frame is right. Straight starter boards, consistent gaps, and seams that land on joists are what separate a pro-looking deck from a wavy one.
DifficultyIntermediate
TimeA weekend for the boards on a typical deck, once the frame is done
SkillsComfortable with a drill and a circular saw; patience for keeping lines straight
PermitsDecking itself usually rides on the framing permit — but the deck as a whole almost always needs one.
Tools you'll need
- Drill/driver and coated deck screws (or a hidden-fastener kit)
- Circular saw or miter saw
- Spacing tool or a couple of 16d nails for gaps
- Chalk line and tape measure
- Pry bar (for straightening bowed boards)
- Orbital sander for any rough spots
Step by step
- Acclimate and sort the boards Let boards sit a few days near the site, then sort out the worst bows for short runs and cuts.
- Start straight off the house Snap a chalk line and fasten the first board dead straight — every board after it follows this one.
- Gap the boards consistently Leave about a 1/8" gap between boards for drainage and expansion (pressure-treated boards can be butted tighter since they shrink as they dry).
- Stagger seams over joists Any end-to-end seam must land on a joist, and stagger seams between rows so they don't line up.
- Fasten and trim Two screws per joist (or hidden clips), then run a chalk line and trim the overhang flush in one pass for a clean edge.
- Sand and seal Knock down any splinters, then seal or stain — see the deck stain calculator for how much you'll need.
Common mistakes
No gap between boards
Boards need a drainage and expansion gap or they trap water and cup. Use a spacer for consistency (PT lumber is the exception — it shrinks).
Seams that miss a joist
Every butt seam must be supported by a joist. Plan board lengths so ends land on framing, or add blocking.
Uncoated or wrong-length screws
Use exterior-rated coated or stainless screws long enough to bite ~1" into the joist — interior screws rust and stain.
Forgetting to seal cut ends
Field cuts expose untreated wood. Brush end-cut preservative on cuts for pressure-treated boards.
Safety
- Wear eye protection when cutting — composite and PT dust is irritating.
- Keep fasteners and offcuts off the walking surface as you go.
Frequently asked questions
How big a gap between deck boards?
About 1/8" for dry boards. Wet pressure-treated boards can be installed nearly tight because they shrink as they dry.
How many deck boards do I need?
Enter your deck length, width, and board size above — the calculator returns boards (with 10% waste) plus screws.
Composite or pressure-treated?
Composite costs more up front but barely needs maintenance; pressure-treated is cheaper but wants cleaning and re-sealing every couple of years.
Should I seal a new deck?
Seal composite never; seal pressure-treated after it dries out (often a few weeks to months), then re-coat as needed.