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Ledger Lag Screw Shear Count Calculator

Calculate how many ledger lag screws are needed for a given total shear load and per-fastener rated capacity.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Lag screws needed

9 screws

Check your inputs

Use the actual IRC/NDS-table or manufacturer rated capacity for your specific screw diameter, species, and ledger/rim board thickness combination — this calculator only divides your total load by whatever per-fastener value you enter.

With the figures above, the lag screws needed comes to 9. The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Deck ledger lag screw shear capacity is governed by NDS/IRC fastener tables specific to screw diameter, species, and ledger/rim board thickness — this calculator divides your total required shear load by your own fastener's rated capacity from that table

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Where does the per-fastener capacity value come from?
It comes from the applicable NDS/IRC fastener table for your specific screw diameter, wood species, and ledger/rim board thickness, or from the fastener manufacturer's published data — this calculator does not look that value up for you.
Why does the result round up?
You can't install a fraction of a lag screw, so the required count is rounded up to the next whole screw to ensure the total rated capacity meets or exceeds the required shear load.
Does this account for spacing and edge distance requirements?
No — this only calculates the number of screws needed for shear capacity. Fastener spacing, edge distance, and staggering pattern must be checked separately against code requirements.