Deck and fence calculator: what do I need?
Boards, joists, screws, posts, pickets and concrete bags from your measurements. Free, no sign-up, and nothing you type leaves your browser.
Filled in from IRC R507.7 (2021 and 2024), read Oct 4, 2026: at least two per board at each joist.
This page counts pieces at the spacing you give it. It doesn't check sizes, spans or footings. Your plan, your building department or a deck builder does.
IRC R507.3.2: deck footings at least 12 in below undisturbed ground. R507.3.3: decks attached to a frost-protected structure need below-frost footings, solid rock or another approved frost-protection method.
The post
The post
Deck shopping list
Type your deck's size and boards to see the shopping list.
Still needed
Clear the deck tab?
Your browser blocked copying. Select the text below and copy it.
Measure twice, and confirm with your supplier before you order.
Rather have it built? Find a deck builder near you.
How the deck and fence calculator works
You give it the numbers off your tape and your plan, and it gives back a list you can buy from. Pick the Deck or Fence tab and type what you measured. Every line of the list shows the arithmetic behind it, so you can check it at the counter before anyone rings it up.
It counts. It doesn't design. The joist spacing, the post spacing and the depth of your footings come from your plan or your building department, and the calculator takes them as given. Two figures arrive filled in, each with its source beside it: joists 16 in apart, and two fasteners in every board at every joist. Both come from the deck section of the International Residential Code. Both are yours to change.
Widths are the ones you measure. Under the American Softwood Lumber Standard, a board sold as 6 in wide measures 5 1/2 in dry, and on a 12 ft deck that half inch is worth two rows of boards. The chips under the width fields fill in the dry sizes. Your tape still gets the last word, because wet lumber runs a little wider.
The arithmetic is exact and rounds once, at the end. Rows, joists and posts round up to whole pieces. Any extra for waste goes onto whole boards or pickets and gets rounded up again. Concrete bags come from the total volume on your screen and the yield printed on your bag, counted once for the whole job.
Deck calculator: boards, joists and screws
A deck board has to end on a joist, or there's nothing under the end to screw into. So when your deck runs longer than your boards, the calculator cuts each board back to the last joist it reaches. The short piece that finishes the row comes from an offcut if one is long enough, and from a fresh board if not.
That's why board length matters more than square footage suggests. Take a 20 by 12 ft deck with joists 16 in apart. In 10 ft boards it takes 56, in 12 ft boards 52, in 16 ft boards 33 and in 20 ft boards 26. Divide the length by the board length instead and you'd buy 52, 44, 33 and 26. The 12 ft boards are the ones that bite: every row needs an 8 ft piece, and the 4 ft left over fits nowhere. Retype the board length and compare now, while changing your mind costs nothing.
Every board gets two fasteners at every joist it crosses, the minimum in IRC section R507.7, and two more at each butt joint, because both ends need holding down. A 16 by 12 ft deck in 16 ft boards comes to 676: 26 rows, 13 joists, two each. For hidden clips, type the clip maker's count instead.
Fill in the posts block and you also get the posts along each beam, at the spacing in your plan, plus the concrete for their holes. It won't pick that spacing, the beam or the footing size for you: those come from load tables and your soil. The IRC puts deck footings at least 12 in below undisturbed ground. If the deck is attached to a frost-protected structure, its footings also need frost protection: below the frost line, on solid rock or another approved method.
Fence calculator: posts, rails, pickets and concrete
Type each straight run as its own stretch, measured post center to post center, and add your gates as openings. A stretch ends wherever the fence stops, turns or meets a gate. The calculator spaces line posts evenly along each stretch, never farther apart than your spacing, then names every post by its job: line posts in the middle of runs, and end, corner and gate posts where runs stop or turn. A fence with two ends needs one more of those than a fence that goes all the way around.
Ready-made panels raise one question, so the calculator asks it out loud: do they hang between the posts or across their faces? Between the posts, every section is a panel plus a post. With 8 ft panels and 4x4 posts that's 8 ft 3 1/2 in center to center, and a 66 ft run takes 8 panels instead of 9.
Concrete is worked out hole by hole: the hole's volume, less the post when it sits in the concrete, then the whole fence's total, then bags. The example fence, 22 posts in 10 in holes 24 in deep, needs 20.26 cu ft, or 46 bags at 0.45 cu ft each. Round up to three bags a post and you'd haul 66, and your back pays for the difference. One maker's own rule runs the other way. Quikrete's data sheet says two 50 lb bags set a 3 in post in a 9 in hole 30 in deep. Work the hole out and, less the post, it holds about 0.95 cu ft, or 0.82 if you stop 4 in short of the top, as the same sheet allows. Two bags yield 0.75. We go with the geometry.
Wet concrete burns. The bag's own warning reads "Causes severe skin burns and serious eye damage", so wear gloves and eye protection.
Who this is for
You've staked out a deck or a fence and you're about to buy for it. Or you're holding a contractor's materials list and want to know whether it adds up. Either way, you've got the measurements and the plan, and what you want is the count.
The calculator stops at counts. For the floor area of a deck or a patio, use the square footage calculator. Pouring a slab or footing pads by the yard rather than filling post holes? The concrete calculator works in cubic yards and bags.
Homeowner questions about decks, fences and concrete
How many deck boards do I need for a 12x16 deck?
A 16 by 12 ft deck with the boards running the 16 ft way takes 26 rows of 5 1/2 in boards with 1/8 in gaps: 144 in divided by 5 5/8 in is 25.6, so 26. In 16 ft boards that's 26 boards, one per row. Turn the boards the other way, 12 ft boards across 16 ft, and it's 35. So settle which way the boards run before anything else.
How many joists for a 16 foot deck?
Thirteen at 16 in on center: 192 in divided by 16 is 12 spaces, and 12 spaces have 13 joists, counting both ends. At 12 in on center it's 17. The spacing comes from your plan and your boards. The IRC's table gives 16 in for 1 1/4 in thick wood boards laid square across three or more joists, and composite boards print their own span on the label.
Do deck boards need to end on a joist?
In practice, yes. A board end with no joist under it has nothing to be fastened to, and IRC section R507.7 calls for two 8d nails of the specified type or two No. 8 wood screws at each support. One more catch: a short piece resting on only two joists counts as single span in the IRC's table, where 1 1/4 in thick boards get 12 in on center, not 16.
What is the actual size of a 2x6?
1 1/2 by 5 1/2 in, dry. NIST's American Softwood Lumber Standard (PS 20-25) sets those minimum dressed sizes at manufacture; green lumber usually runs a little bigger, 5 5/8 in for a 6 in width, with different green sizes for redwood and cedar. Deck boards sold as 6 in wide measure 5 1/2 in too. Type 6 instead of 5 1/2 and a 12 ft deck comes out two rows short, 24 instead of 26.
How many fence posts do I need?
Each straight run needs one fewer line post than its sections. Add the end, corner and gate posts once, sharing a post where runs meet. A straight 100 ft fence with posts no more than 8 ft apart has 13 sections, so 12 line posts and 2 end posts: 14 in all. Every corner and every gate adds posts. The example fence, 138 ft in four stretches with one gate, takes 22.
How many fence pickets per 8 foot section?
Eighteen for a privacy fence of 5 1/2 in pickets butted tight: 96 in divided by 5 1/2 is 17.45, and the last one gets ripped. With 3 1/2 in pickets and 2 1/2 in gaps it's 16, since each picket and its gap take 6 in. Measure a picket before you count: one sold as 6 in wide is 5 1/2 in dry.
How many bags of concrete per fence post?
It depends on the hole and on the yield printed on your bag. A 10 in hole 24 in deep with a 4x4 set in it holds 0.92 cu ft, just over two 60 lb bags at 0.45 cu ft each. Count the whole fence, though: 22 such posts need 46 bags, where three a post makes 66. The bag's weight won't tell you: one maker's 80 lb bag yields about 0.60 cu ft, another's lightweight 80 lb bag 0.92 (Sakrete's data sheet for its Maximizer mix, as we read it on October 8, 2026; its product page words the coverage differently).
Do fence panels go between the posts or on them?
Both kinds are sold, and the answer changes your count. Between the posts, each section is a panel plus a post: 8 ft panels with 4x4 posts land the posts 8 ft 3 1/2 in apart, and a 66 ft run takes 8 panels. Fixed across the post faces, a section is the panel width, 8 ft, and the same run takes 9. Ask the store which way yours are made to hang.
How deep should deck footings be?
At least 12 in below undisturbed ground under IRC section R507.3.2. A deck attached to a frost-protected structure also needs frost protection: below the local frost line, on solid rock or another approved method. Your building department decides which edition applies and which method your plan needs. The depth field stays empty for you to fill from that plan.
Do I need to call 811 before digging post holes?
Yes. 811 calls itself "the free national before-you-dig service" and asks you to get in touch "a few business days before you begin any digging", fences included. Utilities then mark their buried lines with paint or flags. Wait until every one of them has answered before the first post hole goes in.
Lumber calculator for a deck or fence: measure first
Measure the deck along the side the boards will run and along the side the joists will run, and write down which is which. Then measure each straight run of fence on its own, from where one post will stand to where the next end, corner or gate post will stand, and leave the gates out of the runs.
Next, measure one of everything you'll buy: a deck board across its face, a picket, a post. Tags carry nominal sizes. Tapes don't.
Last, take the joist spacing, the post spacing and the footing depth from your plan or your building department. Those three numbers decide whether the deck stands up. The rest only decide how many trips you make to the lumberyard.
Sources and last checked
- Deck board fastening, joist spacing, composite labels and footing depth: International Code Council, International Residential Code 2021 and 2024, sections R507.7 and Table R507.7, R507.2.2.1, R507.3.2 and R507.3.3. Figures read October 4, 2026; the 2018 edition was not checked. The code's online library now lists a later printing of the 2024 edition, which wouldn't open for us when we tried on October 8, 2026.
- Lumber sizes and lengths: NIST, PS 20-25 American Softwood Lumber Standard (January 2025), Table 3 and sections 5.3.1 and 5.3.2. Read October 7, 2026.
- Bag yields and the post-setting method: Quikrete Fast-Setting Concrete Mix data sheet 1004-50 (revised November 2025) and Concrete Mix data sheet 1101 (revised October 2022); Sakrete Maximizer Concrete Mix technical data sheet. Read October 7, 2026.
- Calling before you dig: 811 Before You Dig, a Common Ground Alliance initiative. Read October 7, 2026.
Last checked: October 7, 2026 (deck-fence-reference version 2026-10-07).
More free tools for your project
- All free tools on Industry Oversight
Everything else we've built for home and trade jobs, free and in one place.
- Stair calculator: steps down from a deck or porch
For when the deck sits high enough to need steps down to the yard.
- Landscaping material calculator: gravel under a deck, mulch and sod
For the stone under the deck and the beds around it, once the frame is up.