Loan Deck Material Estimator
Enter your deck's length and width to estimate deck boards, joists, screws, and concrete footings — a solid shopping list before you head to the lumber yard.
| Deck area | 0 sq ft |
| Joists (16″ on center) | 0 |
| Deck screws | 0 |
| Concrete footings | 0 |
| 80-lb concrete bags | 0 |
How it works
Assumptions: 5.5″-wide deck boards with a ⅛″ gap (5.625″ effective width), boards laid across the deck width. Board count = length ÷ 5.625″, rounded up. Joists run 16″ on center along the length. Screws: 2 per board per joist. Footings: roughly one per 50 sq ft, with two 80-lb concrete bags each.
Formula & worked example
Formula: Boards = deck length in inches ÷ 5.625 in (a 5.5-in board plus its gap), rounded up. Joists = floor(deck length in inches ÷ 16) + 1, for 16-in spacing; screws = boards × joists × 2. Footings = deck area ÷ 50 sq ft, rounded up, with 2 bags of concrete per footing.
Worked example: A 16 ft × 12 ft deck covers 192 sq ft: 192 ÷ 5.625 rounds up to 35 boards, with 13 joists, about 910 screws, 4 footings and 8 bags of concrete.
When to use this
- You are sketching a backyard deck and need a lumber-yard list — boards, joists, screws, footings — before you talk to anyone about building it.
- A deck quote arrived as one lump sum and you want the material counts underneath it to see whether they are sane.
- You are replacing a deck surface on an existing frame and want the board and screw counts without the guesswork.
- You are staging the project over two weekends and need to know what has to be on site for the framing stage alone.
How to use it, step by step
- Enter the deck length and width in feet — length is the side the board count is worked from.
- Choose a board length that can span your deck width in one piece where possible.
- Click Estimate materials.
- Read boards first, then joists, screws, footings and concrete bags as one list.
- Add your own margin for cuts and damaged boards before you order — the estimator counts the ideal deck.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Deck length | The side divided into board rows | 16 ft is the page default |
| Deck width | The span each board runs across | 12 ft is the page default |
| Board length | Stock length you will buy, chosen from the list | 8, 10, 12 or 16 ft |
| Board width (built-in assumption) | A 5.5 in board plus a 1/8 in gap, 5.625 in of deck per board | Fixed — the estimator does not take other board widths |
Another worked example
A 20 by 14 ft deck covers 280 sq ft. The estimator calls for 43 boards in 16 ft lengths, 16 joists at 16 inch spacing, about 1,376 deck screws, 6 concrete footings and 12 bags of 80-lb concrete. The screw count surprises most people on a deck this size — it is simply 2 screws at every board-to-joist crossing, and 43 boards crossing 16 joists adds up fast.
Frequently asked questions
How many deck boards do I need?
Divide the deck length (in inches) by 5.625 (a 5.5″ board plus a ⅛″ gap) and round up. A 16-ft-long deck needs about 35 boards.
How many screws per deck board?
Two screws at every joist crossing. For 16″-on-center joists, a 12-ft board needs about 20 screws.
How deep should deck footings be?
Footings must extend below your local frost line — commonly 36″ deep in cold climates. Always check local building code and permits first.
What if my deck is wider than the longest board I can buy?
This estimator assumes each board runs the full width in one piece, so pick a board length that covers your width — for a 14 ft wide deck, that means the 16 ft option. If your width beats every stock length, you will be butt-jointing boards over a joist, and the simple board count no longer tells the whole story; plan the layout with your lumber yard rather than stretching this estimate.
What materials are not on this list?
The frame beyond the joists: rim joists, beams, posts, ledger board, joist hangers, flashing and railing are all outside the count, and footing depth is set by your local frost line and permit, not by this page. Treat the output as the decking-and-footings shopping list, then build the framing list separately before the first trip.
Should I order extra boards beyond the count?
Yes — the estimator counts a perfect deck with no miscuts, no warped boards and no end waste, and the page's own guidance is to buy about 10% extra. Lumber yards take returns on clean, uncut stock far more happily than they expedite a Sunday-morning emergency run for three boards.
🛠️ More project math
Figure out paint for the railing with the paint coverage calculator, or compare lumber prices per board foot.