How Many Boards and Screws Are Needed to Build a Deck?

Building an outdoor deck is a great way to increase your home's value and improve the look of your home's exterior. A well-constructed wooden deck creates an inviting extension of your home. The cost of constructing a deck depends on the amount of wood used to build the lower frame and deck surface, the support beams, and the screws and bolts.

If you know just the dimensions of your deck, you can use the calculator on the left to estimate the length of boards and number of screws needed for the frame and upper part of the deck. (The amount of materials needed for the support beams, railing, and steps depends on the deck design, so you must calculate this separately. Use the Deck Railing Calculator to estimate the wood and screws needed for the rail.)

Estimating Wood and Screws for the Lower Frame

If the width parallel to the joists is W feet, the length perpendicular to the joists is L feet, and the spacing between the joists is J inches, then the length of board needed for the frame is

12LW/J + W + 2L (feet).

The number 12 is for converting joist inches to feet. Assuming that you put two screws per joint, the number of screws needed for the frame is at least

412L/J + 4.

You may need more if you double the joists. Always add about 3%-5% extra for wood and screws so you don't run short of building materials. It is better to have wood and screws left over than to come up short.

Estimating Wood and Screws for the Deck Surface

If the width of the boards is a inches and the spacing between them is b inches, then the total length of board needed to surface the top part of the deck is

L(12W + b)/(a + b). (feet).

If your value for b = 0, then the formula is simply

12LW/a (feet).

If you are laying the boards straight, add a 3%-5% waste factor to make sure you have enough supplies. If you are laying the boards at 45 degree angles to the frame, add an extra 8%-10%. Next, assuming two screws per joint, the number of screws needed to secure the top of the deck to the frame is

2(12W + b)(12L + J)/[J(a + b)].

Again, if b = 0, the formula is just

24W(12L + J)/(Ja).

However, if you are laying the boards at a 45 degree angle to the frame, the number of screws needed is approximately

1.5(12W + b)(12L + J)/[J(a + b)] + 2.9(12L + b)/(a + b).

Once again, if b = 0, the formula is simplifies to

18W(12L + J)/(Ja) + 34.8L/a.

© Had2Know 2010