Deck Screw Calculator
Every board crosses every joist, and each crossing takes screws. Give the calculator your deck size, board width and joist spacing for an exact screw count and box count.
Result
- Board rows26rows
- Joists crossed per row13joists
- Screws needed744screws
- Screws per sq ft3.88/sq ft
- 5 lb boxes (~350 screws)3boxes
How it works
screws = rows × joists-per-row × screws-per-joist × (1 + spare%)
- Rows = ceil(144 in ÷ 5.625 in) = 26
- Joists per row = ceil(192 in ÷ 16 in) + 1 = 13
- Base screws = 26 × 13 × 2 = 676
- With 10% spares = 744 screws → 3 boxes of 350
How the deck screw calculator works
Deck screws go where boards meet joists — two per crossing in most builds, driven just inside the board edges to avoid splitting.
The count depends on geometry: rows across the deck width times joists along the run times screws per crossing. Closer joist spacing means more crossings and more screws.
Buy 10% extra. Screws snap, heads strip and one always rolls into the grass. Boxes of 350 (about 5 lb of 2.5" screws) are the standard pack size.
Formula
screws = rows × joists-per-row × screws-per-joist × (1 + spare%)
Worked example: 12 × 16 ft deck, 2 screws per joist
- Rows across 12 ft width = ceil(144 ÷ 5.625) = 26 rows
- Joists along 16 ft at 16" o.c. = ceil(192 ÷ 16) + 1 = 13
- Base screws = 26 × 13 × 2 = 676
- With 10% spares = 744 screws → 3 boxes of 350
- Per square foot = 744 ÷ 192 ≈ 3.9 screws/sq ft
Screws per square foot (2 per joist, 5.5" boards)
| Joist spacing | Screws per sq ft | 200 sq ft deck | 5 lb boxes (~350) |
|---|---|---|---|
| 12" o.c. | ~5.1 | 1,020 | 3 |
| 16" o.c. | ~3.8 | 760 | 3 |
| 24" o.c. | ~2.6 | 520 | 2 |
Includes 10% spares. Boxes of 350 are the common 5 lb pack of 2.5" deck screws.
Frequently asked questions
How many deck screws per square foot?
About 3.8 per sq ft at 16" joist spacing with two screws per crossing and 5.5" boards. At 12" spacing it's closer to 5.1 per sq ft; at 24" about 2.6.
How many screws go in each deck board?
Two screws at every joist the board crosses. A 16 ft board over joists at 16" on center crosses 13 joists, so it takes 26 screws — plus a couple extra at the ends if you're careful about edge spacing.
What size screws should I use for decking?
2.5 inch screws for 5/4 or 1" nominal decking; 3 inch for full 2" thick boards. Use screws rated for pressure-treated lumber (coated or stainless) — bare steel reacts with the copper in the treatment.
Screws or hidden fasteners?
Screws are cheaper, faster and easy to repair. Hidden clips cost more per sq ft but leave no visible heads. Composite decks usually use clips; wood decks usually face-screw or nail.