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Basis: IRC 2021 · R507 (Decks) · R312 (Guards) · Table R401.4.1 (soil) · prescriptive tables only

Deck Framing Calculator

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The deck calculator is fully usable — joists, beam, posts, footings and the whole cut list stay on screen. Your inputs are kept in this browser automatically.

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Site profile

Choose your state to load site values. Nothing is assumed until you do.

Choose your state to load site values.

Footing diameter is the load divided by the soil's bearing value, and the holes are dug below the frost line. Neither is assumed here.

Load path — how the weight gets to the ground
HouseCarries half the deck through the ledger. The band joist beh…4,800 lbLedgerFastener schedule NOT produced — see the code checks.see code checks4,800 lbJoists2x10 spanning 12.0 ft16" o.c.9,600 lbBeam2-ply 2x12posts 8.0 ft apart4,800 lbPosts6x6, 5.0 ft3 total4,800 lb3,200 lb per post × 3Footings18" diameter at 2000 psfdepth not set4,800 lb3,200 lb per footing × 3undisturbed soil

Every pound on the deck travels down this chain. It is only as strong as its weakest link — which on a real deck is almost always the ledger. Amber and red stages have a code check that did not resolve; see the list below.

Code compliance

ENGINEERING REQUIRED

This design needs a licensed designer.

InputsVERIFICATION REQUIRED

Every dimension needed for this calculation has been given and is usable.

Joist size and span (2x10 at 16" o.c.)VERIFICATION REQUIRED
Your span: 12'Maximum allowed: 13' 11"Margin: 1' 11"

Spans 12', within the 13' 11" maximum we compute. That figure has not been verified against the printed table yet, so check it against your code book before you build.

IRC 2021 Table R507.6 — deck joist spans· this rule is marked unverified in our data, so it cannot return a PASS

Beam span between posts (2-ply 2x12)VERIFICATION REQUIRED
Your beam span: 8'Maximum allowed: 9' 1 3/16"Margin: 1' 1 3/16"

Beam span of 8', within the 9' 1 3/16" maximum we compute. That figure has not been verified against the printed table yet, so check it against your code book before you build.

IRC 2021 Table R507.5 — deck beam spans· this rule is marked unverified in our data, so it cannot return a PASS

Soil bearing capacity — 2000 psf assumedNEEDS MORE INFO

EVERY FOOTING SIZE BELOW DEPENDS ON THIS NUMBER, AND IT IS AN ASSUMPTION. 2000 psf is a presumptive value the code lets you assume — it is not a measurement of your ground. Soft or filled ground can be well under half of it, which doubles the footing area you need. Confirm it with your building department or have the soil tested, then tick the box.

IRC 2021 Table R401.4.1 — presumptive load-bearing values· this rule is marked unverified in our data, so it cannot return a PASS

Footing depth below frostNEEDS MORE INFO

Frost depth has not been given, so the footing depth cannot be checked. It is set by your local frost line, which varies enormously — ask your building department.

IRC 2021 R403.1.4 — footings below the frost line· this rule is marked unverified in our data, so it cannot return a PASS

Ledger fastener scheduleENGINEERING REQUIRED

NOT PRODUCED. A ledger fastener schedule must come from the printed table for your exact case — fastener type, diameter, edge and end distances, row spacing and the band-joist material all change it, and none of that follows from the joist span alone. This app has not transcribed IRC Table R507.9.1.3(1), so it will not guess one. Use AWC DCA6 (free at awc.org) or the printed R507.9.1.3, or have the connection designed.

Lateral load connectionENGINEERING REQUIRED

NOT PRODUCED. IRC R507.9.2 requires a lateral load connection — hold-down tension devices tying the deck framing back into the house framing, not just the ledger bolts. The device capacity and placement are not loaded in this app and will not be inferred. Specify them from DCA6 or an engineer.

Post height (6x6)VERIFICATION REQUIRED
Your post height: 5'Maximum allowed: 14'Margin: 9'

Post height of 5', within the 14' maximum we compute. That figure has not been verified against the printed table yet, so check it against your code book before you build.

IRC 2021 R507.4 — deck posts· this rule is marked unverified in our data, so it cannot return a PASS

Guard heightVERIFICATION REQUIRED
Minimum required: 36"Your guard height: 36"Above the minimum by: 0"

Guard height of 36", at or above the 36" minimum we hold. That limit has not been verified against the printed code yet, so check it against your code book before you build.

IRC 2021 R312.1.2 — Minimum guard height· this rule is marked unverified in our data, so it cannot return a PASS

Checked against IRC 2021 · IRC R507. These checks are an aid, not an approval — your building department has the final say.

HOUSELEDGER(2) 2x12 BEAM3 posts on 18" footings2'2x10 @ 16" o.c.16'12'
Deck framing plan — 13 joists, 2x10 at 16" o.c., (2) 2x12 beam on 3 posts

Southern-Pine — sized as Hem-Fir; NDS Table 4B not yet loaded

You chose Southern Pine, but its design values are size-specific (NDS Supplement Table 4B) and are not loaded in this app yet. The size below was solved against Hem-Fir, the weakest species we hold values for — so it is conservative, and a real Southern Pine member of the same size will be stronger. It is not the answer the Southern Pine tables would give.

2x10 joists at 16" o.c.Verification required · 86% used
Spans 13' 11"You need 12'

Limited by bending strength.

Assumptions applied

Computed from NDS design values with wet-service factors applied, against IRC 2021 Table R507.6 (deck joists) — L/360, no2 hem-fir (substituted), governed by bending. Not a confirmed R507.6 cell: the deck table itself is not loaded, so this is the solved equivalent and must be checked against the printed table.

13 × 2x10
Joists
(2) 2x12
Beam
3
Posts
—
Footing dia.
96"
Post spacing
10
Guard posts

⚠ Ground snow load — not available. Choose your state to load site values.

⚠ Frost depth — not available. Choose your state to load site values.

⚠ Soil bearing — not available. Choose your state to load site values.

⚠ Southern Pine design values are size-specific (NDS Table 4B) and are not loaded yet, so Southern Pine is sized against the more conservative Hem-Fir values. Verify against the Southern Pine span tables.

⚠ Joists are exposed to weather — wet service adjustment factors were applied.

⚠ Ledger fastener schedule and lateral load connection were NOT generated — see the code checks. These are the two connections decks actually fail at.

Cut list

Not for purchase — this design needs an engineer

This design is outside the prescriptive tables, so the quantities below are not a code-compliant answer. They are not an order.

ComponentQtySizeLength
deck joist132x1012' 3"
deck rim joist22x1016'
deck beam22x1216'
deck post36x65'
guard post104x44'
guard rail1 splice per member

2 pieces spliced end to end per member — 40.0 ft is longer than the 20 ft maximum stock length. 1 splice per member; the splice connection is not designed here.

42x420'
decking board262x616'
Estimated total board footage: 950.4 bd ft

Not on the shopping list

These members are waiting on a compliance check. Nothing here has a quantity you should order — buying against an unresolved check is how the wrong part ends up on site.

deck ledgerLedger and its fastener schedule — specify by design professional, not included in takeoff

Optimized cut list (minimized waste)

60
Boards to buy
846 ft
Total stock length
71.8 ft
Estimated waste
8.5%
Waste rate

Deck Framing Calculator

Size a deck from the house out. Enter the width along the house, how far it projects, the joist spacing and whether it hangs off a ledger or stands free, and the calculator returns joists, beam size and ply count, post spacing and size, footing diameters, decking boards, guards and hardware.

It also draws the load path — House, Ledger, Joists, Beam, Posts, Footings — with the load each stage carries and the spacing on each. That chain is the thing most people building their first deck cannot see: every pound standing on the surface has to reach solid ground through it, and it is only as strong as its weakest link.

On a real deck that weakest link is the ledger. Decks do not usually fail in the field of the joists; they come off the house all at once, with people on them. This calculator will NOT generate a ledger fastener schedule or a lateral load connection by inference — it returns engineering required and points you at the printed table, because a schedule that looks authoritative and is not is worse than no schedule.

Which code tables this works from

IRC Table R507.6 — deck joist spans
Joist spans for exterior exposure. Deck joists carry 40 psf live plus 10 psf dead and are wet-service, which shortens them against an interior floor joist.
IRC Table R507.5 — deck beam spans
Beam span between posts, keyed on the joist span the beam carries.
IRC R507.9.1.3 — ledger fastener schedule
Fastener type, diameter and spacing for attaching a ledger to a band joist. Not transcribed here, so no schedule is produced — see AWC DCA6, which is free.
IRC R507.9.2 — lateral load connection
Hold-down tension devices tying the deck framing back into the house. A different job from the ledger bolts, and also not inferred.
IRC Table R401.4.1 — presumptive soil bearing
Sets the footing diameter. Every footing size scales directly with it, so it is shown next to the footing result with a confirm gate.

The inputs that matter

Projection from the house
This is the joist span, and it drives the joist size, the beam size and how many footings you dig. Shortening it is usually the cheapest fix for an expensive deck.
Ledger-attached or freestanding
A freestanding deck replaces the ledger with a second beam line on posts. It is more lumber and more holes, and it removes the connection decks actually fail at.
Soil bearing capacity
A presumptive value is permission to assume, not a measurement of your ground. Halve it and the footing area doubles.
Height above grade
Decides whether a guard is required, and how tall the posts are. Tall posts need bracing whatever their size.

Common questions

How far can deck joists span?

Less than an interior floor joist of the same size, because deck framing is exposed to weather and takes wet-service adjustment factors. A 2x8 that reaches nearly 13 feet inside will fall short outside. Enter your species, grade and spacing and the calculator checks the size you intend to use rather than picking one for you.

What size footings do I need for a deck?

It depends on the load each post carries and the bearing capacity of your soil. The load comes from the tributary area — roughly half the joist span times the post spacing — and the required bearing area is that load divided by the soil bearing value. Footing depth is a separate question, set by your local frost line.

How do I attach a deck ledger to the house?

From the printed table for your exact case, not from a rule of thumb. Fastener type, diameter, edge and end distances, row spacing and the band-joist material all change the answer, and none of it follows from the joist span alone. AWC DCA6 is free and has the tables; most building departments hand it out. Flashing and the condition of the band joist behind the siding matter as much as the fasteners.

Do I need a lateral load connection on a deck?

The IRC requires one on a deck attached to a house. It is hold-down tension devices tying the deck framing back into the house framing — a different job from the ledger bolts, which resist gravity and withdrawal. The lateral connection resists the deck being pushed away from the house. Specify it from DCA6 or an engineer.

GoFramePro provides preliminary planning and estimating information. Confirm structural requirements, local amendments and permitting requirements with the authority having jurisdiction.

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