Ledger fastener count calculator
This tool counts fasteners. It does not choose the spacing, the diameter or the fastener — those come from the attachment table for your specific assembly, and getting them wrong is how a ledger pulls off a house. Enter the spacing you were given and it returns the count and layout.
Ledger run
How this is calculated
- Positions per row = ⌈(length − 2 × end distance) ÷ spacing⌉ + 1, which places a fastener at each end and divides what is left.
- Total = positions × rows.
- Actual spacing = (length − 2 × end distance) ÷ (positions − 1). It is always ≤ what you entered, never more.
- Stagger offset = actual spacing ÷ 2. The second row is shifted by half a position so no two fasteners sit in the same grain line.
Worked example
A 24 ft ledger, 16″ spacing, two rows, 2″ end distance:
- Usable length = 288 − 4 = 284″
- Positions = ⌈284 ÷ 16⌉ + 1 = 18 + 1 = 19 per row
- Total = 19 × 2 = 38 fasteners
- Actual spacing = 284 ÷ 18 = 15.8″, so you are inside the 16″ you were given
- Boxes at 50 per box = 1, with 12 spare
The three things that actually cause ledger failures
Fastener count is the easy part. The failures come from somewhere else:
- Fastening through the siding. A ledger must bear on the house framing, not on vinyl or fibre-cement siding. Standoffs and flashed spacers exist for this and are not optional.
- Missing the rim or band joist. Fasteners must hit solid framing. A 24 ft ledger with two fasteners per bay that both miss the joist is a 24 ft ledger held by friction.
- No flashing sequence. Water behind the ledger rots the band joist, and the ledger then has nothing to hold. The order — flashing tape, Z-flashing, cap — matters more than the fastener pattern.
If the attachment is to brick veneer, stone or a cantilevered floor, the ledger approach may be wrong entirely and a freestanding deck with its own posts is the answer. That decision is not arithmetic.
What a fastener count cannot tell you
- It does not determine spacing, diameter or fastener type. Those come from IRC Table R507.9.1.3 or an engineered detail for your wall assembly. Use the table, then come back here for the count.
- It does not check edge distance or penetration beyond the simple end allowance.
- It does not count joist hangers, rim connections or hold-downs, which are separate schedules.
- It does not validate the wall. A ledger on a 2×4 wall, or on a wall with no rim joist, needs a different detail.
Questions people actually ask
How many lag screws do I need for a 24 foot ledger?
At 16 inches on centre in two rows, 38: nineteen positions per row, with the first and last 2 inches in from each end. That is a count, not a specification — the spacing has to come from the attachment table for your wall.
Should ledger fasteners be staggered?
Yes. Offsetting the second row by half the spacing keeps two fasteners out of the same grain line, which reduces splitting along the ledger and spreads the load more evenly into the band joist.
Can I attach a deck ledger to brick veneer?
Generally no. Brick veneer is not structural and will not hold a ledger. In that case the deck is built freestanding with its own posts and beam, or the ledger is attached to the framing behind the veneer with an engineered detail.
Lag screws or structural screws for a ledger?
Both are used, and both have published code recognition when installed per the manufacturer. What fails is using the wrong diameter, the wrong length, or a decorative lag that does not reach the framing.