Skip to content
Request a ToolBrowse all tools
Home / Joinery & Furniture Engineering / Screw Spacing Calculator
Vriksai Timber Intelligence

Screw Spacing 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

Edge and end distances decide whether the timber splits. In dense hardwood the spacing is only achievable with pre-drilling.

NDS 2018 USAIS 883 IndiaEurocode 5 EUAS 1720 AUPDF Report
🔩

Screw Spacing — 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.

Standard, Fastener & Load
Dimensions
mm
mm
pcs
✓
Minimum Spacing & Distances
—
mm
Spacing in Row (a1)
—
mm
Row Spacing (a2)
—
mm
End Distance, loaded (a3,t)
—
mm
Edge Distance, loaded (a4,t)
Formula Trace
Engineering note Spacings follow EC5 and IS 883 geometry for the inputs shown. They prevent splitting; they do not confirm the connection carries the load. Final structural design must be verified by a qualified engineer against your local code.
📏 Screw Spacing Calculator
Gives the minimum spacing, end distance and edge distance for screws, nails and bolts in timber connections — the six code distances that decide whether a joint holds or the wood splits. Includes a layout check that fits your fastener count into the member.
Where Used?
Structural TimberLedger BoardsDecking FramesTrusses & GussetsFurniture JointsPergolas
Formulas
EC5 Table 8.2 (nails) — e.g. a1 = (5+5|cosα|)d, a3,t = (10+5cosα)dEC5 Table 8.4 (bolts) — a1 = (4+|cosα|)d, a3,t = max(7d, 80 mm)EC5 8.7.2 — screws d ≤ 6 mm follow nail rules, d > 6 mm follow bolt rulesIS 883 bolted — row spacing 4d, rows 4.5d, loaded end 7d
About the Screw Spacing Calculator
Most split boards and failed joints trace back to the same mistake — fasteners placed too close to an edge, an end, or each other. Design codes solved this long ago with minimum distance rules, but the rules change with fastener type, diameter, predrilling and load direction, which is why people end up guessing. This calculator applies the Eurocode 5 tables and the commonly specified IS 883 values directly, then runs a practical layout check: how many rows fit your member width, and how long the joint must be for the fasteners you need. It works as a timber fastener spacing reference for structural screw and bolt connections, and answers the timber connection design questions that generic span tables never cover.
Where Is This Used?
Furniture AssemblyHardware FixingDeck BuildingJoinery ConnectionsIndian Hardwoods
Sources & verification
  • EN 1995-1-1:2004, 8.3.1.2, Table 8.2 — nails, with and without predrilled holes (ρk ≤ 420 kg/m³)
  • EN 1995-1-1:2004, 8.5.1.1, Table 8.4 — bolts
  • EN 1995-1-1:2004, 8.7.2 — screws: d ≤ 6 mm follow the nail rules, d > 6 mm the bolt rules
  • IS 883:2016 — bolted and screwed joints
  • Table values cross-checked against Swedish Wood, “Design of timber structures Volume 2 — Rules and formulas according to Eurocode 5”, UK Edition 1:2022, Table 10.2
Formula checked against the sources above by an automated regression test (tests/verify-phase3b.js) that derives each expected value independently of this page. Last reviewed .
FAQ
What is the quick rule of thumb for screw spacing in wood?
For everyday joinery: keep screws about 10 diameters apart along the grain, 5 diameters from an end and 3 from an edge, and pre-drill hardwoods. Those track the code values closely — this tool gives the exact figures per standard.
Why is the end distance so much bigger when the joint is in tension?
A loaded end is where the wood can shear out in a block ahead of the fastener. EC5 asks up to (10+5cosα)d at a loaded end for non-predrilled nails versus 10d unloaded, and bolts need max(7d, 80 mm). Compression ends can be shorter because the load pushes wood together instead of tearing it away.
Does pre-drilling really let me place fasteners closer?
Yes, substantially. A pilot hole removes the wedge action that splits the wood, so EC5 drops nail spacing from (5+5cosα)d to (4+|cosα|)d and end distance from (10+5cosα)d to (7+5cosα)d. In dense hardwoods pre-drilling is effectively mandatory anyway.
Should I use the EC5 or IS 883 setting in India?
For most Indian site and workshop work, the IS 883 values are what inspectors and older drawings reference. EC5 is more detailed — it distinguishes nail, screw and bolt behaviour and predrilling — so many engineers design to EC5 and check IS. When the two disagree, using the larger distance is never wrong.
Can I stagger fasteners to squeeze more into a narrow member?
Staggering rows lets adjacent fasteners sit closer along the length while keeping true point-to-point distances legal, and it spreads the split risk across growth rings. The row spacing (a2) and edge distances still apply — staggering helps most when member width limits you to one straight row.
ResourcesView the formulasFormula Library
Related Joinery tools
More tools in this category
Sag & Deflection CalculatorShelf and beam deflection under loadGolden Ratio DesignerHarmonious furniture proportions with phiExpansion Gap CalculatorWood movement gaps for panels and topsDovetail GeneratorPin and tail layout for any board
Wood species data
Density, hardness and movement for 60 timbers
Browse all species 
How the calculation works
Every distance is a multiple of the fastener diameter, and the angle to the grain matters because timber splits along the grain far more easily than across it. A loaded end — where the timber could shear out ahead of the fastener — needs roughly twice the distance of an unloaded one.
Show the formula
EN 1995-1-1 Table 8.2, with all distances as multiples of fastener diameter d and alpha the angle to the grain. Nails not predrilled: a1 = (5 + 5|cos a|)d below 5 mm or (5 + 7|cos a|)d at and above, a2 = 5d, a3,t = (10 + 5|cos a|)d, a3,c = 10d, a4,t = (5 + 2 sin a)d or (5 + 5 sin a)d, a4,c = 5d. Predrilled: a1 = (4 + |cos a|)d, a2 = (3 + |sin a|)d. Per EC5 8.7.2 screws up to 6 mm follow the nail rules and larger screws follow the bolt rules.
Table 8.2 assumes rho_k up to 420 kg/m3. Between 420 and 500 the code requires wider spacing, and above 500, or above 6 mm diameter, it requires predrilling. This checks geometry only, not whether the connection carries the load.
References and what each one provides
  • EN 1995-1-1 (Eurocode 5)CENTable 8.2 and 8.4 spacing, edge and end distances for nails, screws and bolts.
  • IS 883Bureau of Indian StandardsIndian code of practice for design of structural timber, including permissible stresses, joint design and deflection limits.
Unverified values are marked as such rather than presented as sourced.
Limitations of this calculation
Geometry rules only, for the fastener and timber entered. It confirms spacing that prevents splitting; it does not confirm the connection carries the load, and does not account for steel plate connections, group effects, or seasoning splits already present.
Do not use this for Connection design, lifting or rigging points, safety-critical fixings, or anything supporting people.
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 strength properties reference.
How to use this tool
  1. Enter your stock sizes below, then press Calculate.
  2. Pick your design standard and fastener type from the dropdown.
  3. Fill in fastener diameter, member width, fasteners needed. 
  4. Press Calculate. 
Worked example
With the tool's starting values — fastener diameter = 6, member width = 140, fasteners needed = 8 — pressing Calculate gives: 30 mm (spacing in row (a1)); 18 mm (row spacing (a2)); 72 mm (end distance, loaded (a3,t)). 
Common mistakes to avoid