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Wood Screw Pull-out & Shear Estimator

Estimate withdrawal load and shear capacity for a wood screw by species, diameter, and embedment depth.

Calculator

Oak 0.63, Maple 0.56, Doug-Fir 0.45, SPF 0.36.

0 = perpendicular to grain, 90 = parallel.

What makes this different

Most online 'screw strength' tools give you a single number from the box. This one applies the NDS withdrawal formula (1,800 × G^(5/2) × D^(3/4)) for withdrawal and a European yield-model approximation for shear, with species-specific specific gravity.

Who it's for & when to use it

Sizing screws for a deck ledger, a structural hanger, or a heavy wall-mounted cabinet.

How to use

  1. Enter the dimensions of your material or the parameters of your project.
  2. Adjust the optional knobs (waste factor, kerf, planer allowance) to match your shop practice.
  3. Click Calculate and read the output. Use the per-item breakdown for ordering, the totals for budgeting.
  4. Compare the result to your lumber yard's quote — the effective $/BF column is the apples-to-apples number.

Formula: Withdrawal W (lb/in) ≈ 1,800 × G^(5/2) × D^(3/4). Total withdrawal = W × L × angle factor. Shear based on dowel-bearing capacity.

Notes & tips from the shop

  • Specific gravity is the single biggest variable. Two pieces of 'pine' can differ by 30 % in withdrawal strength.
  • Always apply a safety factor of 4–6 for structural connections.
  • Pilot holes slightly smaller than the shank improve withdrawal by preventing fiber separation.

Frequently asked questions

What if my screw is angled?

Withdrawal strength drops fast as you go off-axis. Toe-screws (> 30°) lose 40–60 % of their straight-pull strength.

Does screw length matter more than diameter?

Embedment depth is roughly linear; doubling depth doubles withdrawal. Doubling diameter only multiplies by ~1.7.

Stainless vs coated?

Coatings and stainless affect corrosion, not withdrawal capacity — that's governed by the wood.

Limitations

Single-screw model. Multiple-screw groups, row tear-out, and metal-side plate capacities are not modeled.

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