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Vriksai Timber Intelligence

Screw Strength Calculator

Calculate withdrawal and lateral capacity for wood screws, lag bolts and nails. NDS 2018, Eurocode 5, IS 883:2016, AS 1720 with group factor.

Why this calculation matters

Withdrawal capacity decides how many fixings a load needs and whether end-grain fixing is viable. It is capacity, not working load — your safety factor still applies.

NDS 2018 USAIS 883 IndiaEurocode 5 EUAS 1720 AUPDF Report
🔩

Screw Strength — Calculator

Calculate withdrawal and lateral capacity for wood screws, lag bolts and nails. NDS 2018, Eurocode 5, IS 883:2016, AS 1720 with group factor.

Fastener, Unit & Standard
Fastener Dimensions
mm
mm
pcs
Wood Species & Load Direction
kg/m³
✓
Fastener Strength Results
—
N
Single Fastener
—
N
Group Total
—
kg
Weight Capacity
—
N/mm
Per mm Penetration
Connection Strength Rating
Formula Trace
Engineering note Values are ultimate capacity, not working load, and assume sound timber at the stated density. Apply your own safety factor. Final structural design must be verified by a qualified engineer against your local code.
🔩 Screw Strength Calculator
Determines how much load a wood fastener can carry before failing — axially (withdrawal) or sideways (lateral shear). Critical for safe furniture joints, structural timber connections, decking and cabinet installations.
Where Used?
Furniture AssemblyStructural TimberDeckingDoor HingesShelf BracketsLedger Boards
Formulas
IS 883:2016 — W = k × d × L (k = 12/10/7/5 by density group)NDS 2018 — W = 2850 × G² × D (lbs/in penetration, wood screw)Eurocode 5 — f_ax,k = 0.52 × d^-0.5 × L^-0.1 × ρ^0.8Group factor — Cg = max(0.4, 1 − 0.05×(n−1))
About the Screw Strength Calculator
Not all screwed joints are equal — how much load a screw can hold depends on the wood's density, the screw diameter and how deep it bites into solid timber. Get it wrong and the screw either strips out of soft wood or splits a dense hardwood. This calculator estimates withdrawal and shear capacity using the recognised wood-screw relationships from NDS, IS 883 and Eurocode 5, so you can choose the right screw and penetration depth for the species you're working in. It puts numbers on screw holding power in wood — withdrawal force and lateral values by species, size and embedment depth. For the geometry side of the joint — how far apart and how far from edges — use the companion screw spacing calculator.
Where Is This Used?
Furniture AssemblyHardware FixingDeck BuildingJoinery ConnectionsIndian Hardwoods
Sources & verification
  • IS 883:2016 density groups
  • NDS 2018 withdrawal and lateral capacity
Formula checked against the sources above by an automated regression test (tests/test-calculators.js) that derives each expected value independently of this page. Last reviewed .
FAQ
IS 883:2016 density groups?
Group A (>800 kg/m³) k=12 — Sal, Ebony, Ipe; Group B (601–800) k=10 — Teak, Shisham; Group C (401–600) k=7 — Deodar, Douglas Fir; Group D (≤400) k=5 — Paulownia, Western Red Cedar.
Minimum penetration depth?
Minimum 10× shank diameter in softwoods, 8× in hardwoods. NDS: 2/3 of total length in base member. IS 883: minimum 6D for withdrawal calculations.
Do I really need to pre-drill, or can I just drive screws straight into hardwood?
In dense hardwoods, pre-drilling isn't optional — it's the difference between a sound joint and a split board or a snapped screw. Hard, dry timber doesn't compress to make room for the screw, so the wood splits or the screw shears off, especially near edges and ends. Drill a pilot hole roughly the size of the screw's core (the shaft without the threads) so the threads still bite but the wood isn't forced apart. Softer woods are more forgiving, but even there a pilot hole gives you straighter, stronger, more repeatable results — which is what the holding figures here assume.
ResourcesView the formulasFormula Library
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Wood species data
Density, hardness and movement for 60 timbers
Browse all species 
How the calculation works
All three codes say the same thing in different arithmetic: holding power rises steeply with timber density and roughly in proportion to how deep the thread bites. Diameter matters less than depth, which is why a longer screw usually beats a fatter one in the same timber.
Show the formula
EN 14592 / EC5: f_ax,k = 0.52 x d^-0.5 x l_ef^-0.1 x rho_k^0.8, and capacity = f_ax,k x d x l_ef. NDS 2018: W = 2850 x G^2 x D lb per inch of thread penetration, with G the specific gravity. IS 883: capacity = k x d x l, with k from the density group (12, 10, 7 or 5). Multiple fasteners are reduced by a group factor.
This is ultimate capacity in sound, defect-free timber with NO safety factor applied. The end-grain and angled-load reductions used here are approximations of the code factors. Not a connection design.
References and what each one provides
  • EN 1995-1-1 (Eurocode 5)CENDesign of timber structures: fastener spacing and edge distances, connection capacity, and deflection limits.
  • IS 883Bureau of Indian StandardsIndian code of practice for design of structural timber, including permissible stresses, joint design and deflection limits.
  • USDA Wood Handbook (FPL GTR-190)USDA Forest Products LaboratorySpecies density, which governs withdrawal capacity.
Unverified values are marked as such rather than presented as sourced.
Limitations of this calculation
Ultimate capacity in sound, defect-free timber at the stated density, with no safety factor applied. It is not a connection design. It does not account for load duration, service class, corrosion, cyclic loading, or reduced end-grain capacity unless selected.
Do not use this for Lifting certification, fall-arrest anchorage, rigging, or any life-safety connection. It reports ultimate capacity with no factor applied.
Figures are engineering estimates from the inputs and assumptions shown. Verify against the actual material and, where the result affects structure or safety, against a qualified professional.
Ipe LapachoDensity · Janka · movementIrokoDensity · Janka · movementJarrahDensity · Janka · movement
Full listing in the Janka hardness table.
How to use this tool
  1. Enter your stock sizes below, then press Calculate.
  2. Pick your fastener type and design standard from the dropdown.
  3. Fill in shank diameter, penetration into base wood, number of fasteners, density. 
  4. Press Calculate. 
Worked example
With the tool's starting values — shank diameter = 5, penetration into base wood = 40, number of fasteners = 4, density = 630 — pressing Calculate gives: 2000 N (single fastener); 6800 N (group total); 693.2 kg (weight capacity). 
Common mistakes to avoid