Build a Deck: Calculators in Order
Footings, joists, boards, railing, stairs and cost for a wood deck, in the order you build it.
A deck is built from the ground up, but it is planned from the top down: the size and height you want decide the joists, the joists decide the beam and posts, and the posts decide the footings. Work through the steps below in that order and each result feeds the next.
Start with the footprint and the height of the deck surface above grade. A 12 x 12 ft deck is 144 sq ft, which is why the examples here use it. Height matters more than people expect: above 30 in the code requires a guard at least 36 in tall with gaps under 4 in, and a deck that high needs stairs, so the rise of those stairs is measured from the finished deck surface, not from the joist.
Footings come next because they are the one part you cannot fix later. Their depth has to reach below the local frost line, and their diameter depends on how much load each post carries. Ask your building department for the frost depth; almost every jurisdiction requires a permit for an attached deck and wants the footing size on the drawing.
Joists and beams follow from species, grade, spacing and span, and the span tables in the code are the limit, not a suggestion. Decking is the visible part, but it is bought last and by length, so the least waste comes from planning board lengths against the joist run. Finish with the stain, the railing and the cost, and add each material list to your project list to print one shopping list for the whole deck.
Your numbers
Change the example and every link below opens its calculator with your values.
Set the deck size and height
Enter the footprint and height. The result lists joists, beam, posts, footings and hardware for the whole deck.
Size the footings
Footing diameter follows the load on each post and the soil. Depth has to go below the frost line your building department names.
Check the joist spans
Confirm the joist size and spacing against the code span tables before you buy lumber.
Order the deck boards
Boards are bought by length. Pick the length that wastes the least for your joist run.
Plan the railing balusters
Above 30 in the guard needs balusters spaced so a 4 in sphere cannot pass. Get the count and the exact gap.
Lay out the stairs
Measure the rise from the finished deck surface to the ground and get riser count, tread depth and stringer length.
Buy the stain
Stain covers less on rough or new boards than on smooth ones, so calculate gallons for both sides of the job.
Check the cost
Compare your material list with a low, typical and high price for your state.
My project list
Open a calculator above and choose Add to project under its material list. Lists you save land here, on this device only.
Nothing saved for this project yet.