Joinery
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
- Enter the dimensions of your material or the parameters of your project.
- Adjust the optional knobs (waste factor, kerf, planer allowance) to match your shop practice.
- Click Calculate and read the output. Use the per-item breakdown for ordering, the totals for budgeting.
- 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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