Timber Fastener Spacing Calculator — Nails, Screws & Bolts
Work out the minimum distance a nail, screw or bolt must sit from the end of a board, from its edge, and from the next fixing along. Choose Eurocode 5 or the American NDS, enter the fastener diameter and the direction of the load, and get every distance with the clause it comes from. These are the distances that stop timber splitting — they are not a connection design.
How far apart should screws be in timber?
It follows the screw diameter, not the size of the timber. Eurocode 5 treats a screw of 6 mm (about ¼ in) or less as a nail, so in ordinary softwood without pre-drilling the minimum spacing along the grain is (5 + 5|cos α|)d, where d is the diameter and α is the angle between the load and the grain. A 5 mm (0.2 in) screw loaded along the grain therefore needs 50 mm (2 in) between screws. Screws over 6 mm follow the bolt rules instead, which are far tighter at (4 + |cos α|)d.
How close to the end of a board can I put a nail?
Further than most people leave. Under Eurocode 5 the distance to a loaded end is (10 + 5 cos α)d in softwood with no pre-drilling — fifteen times the diameter when the load pulls straight along the grain. A 3.1 mm (0.12 in) nail needs about 47 mm (1⅞ in); a 4 mm (0.16 in) nail needs 60 mm (2⅜ in). The unloaded end needs 10d. Pre-drilling cuts the loaded figure to (7 + 5 cos α)d.
Does the US code give nail spacing numbers?
No. The NDS publishes numeric edge, end and spacing tables only for bolts, lag screws and drift pins — fasteners of ¼ in (6.35 mm) and over. For nails and wood screws it requires only that distances are "sufficient to prevent splitting of the wood" (12.1.6.6 and 12.1.5.7), and clause 12.5.1.1 fixes the geometry factor at 1.0 below ¼ in so no reduction applies either. US framing takes its nailing from the prescriptive IRC schedule instead.
Minimum geometry, not a connection design. These distances stop the timber splitting. They say nothing about whether the joint carries your load — that needs fastener capacity, member sizes and load cases. Anything structural needs a qualified engineer, and your National Annex or adopted code edition governs. Read the guide →
Minimum distances
Table 8.2 (nails)Installation
- Pointside penetration at least 24.8 mm (8d, smooth nails — 8.3.1.2).
- Nails in end grain cannot be counted on for lateral load (8.3.1.2(3)).
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How the fastener spacing calculator works
- 1Route the fastener to its table: under Eurocode 5 a screw of 6 mm (¼ in) or less follows the nail rules (8.7.1(5)), one over 6 mm (¼ in) follows the bolt rules (8.7.1(4))
- 2Pick the column from the timber density and whether you pre-drill — ρk ≤ 420 kg/m³ (26 lb/cu ft), 420–500 kg/m³, or pre-drilled
- 3Evaluate each distance as a multiple of the diameter d, using the angle α between the load and the grain
- 4Read the unloaded end and edge at α + 180°, which is where the standard defines them
- 5Check pre-drilling: required above 500 kg/m³ (31 lb/cu ft), above 6 mm (¼ in) diameter, or below max{7d, (13d − 30)·ρk/400} thickness
- 6Add the pointside penetration — 8d for smooth nails, 6d for profiled ones
Worked example: a 4 mm nail in C24 softwood
A 4 mm (0.16 in) smooth nail in C24 softwood at ρk = 350 kg/m³, not pre-drilled, with the load running along the grain (α = 0°).
Spacing along the grain 40 mm (1⅝ in), between rows 20 mm (¾ in), to the loaded end 60 mm (2⅜ in), to the unloaded end 40 mm (1⅝ in), to the loaded edge 20 mm (¾ in). Penetration at least 32 mm (1¼ in). Pre-drilling the same joint drops the loaded end distance to 48 mm (1⅞ in) and the spacing to 20 mm (¾ in).
Frequently asked questions
What is α in the Eurocode 5 tables?
The angle between the FORCE and the grain direction — not the angle of the fastener. A screw driven straight into a face still has α = 0° if the load on the joint runs along the grain. Getting this backwards is the most common mistake with these tables, and the required end distance changes by a factor of three between 0° and 90°.
When do I have to pre-drill?
Eurocode 5 requires it when the characteristic density is above 500 kg/m³, when the nail diameter exceeds 6 mm (¼ in), or when the member is thinner than max{7d, (13d − 30)·ρk/400}. Species prone to splitting — the standard names fir, Douglas fir and spruce — use a stricter thickness again. The hole must not exceed 0.8d (clause 10.4.2(3)).
How deep does the fastener have to go into the far piece?
Eurocode 5 asks for at least 8d pointside penetration for smooth nails and 6d for profiled or ring-shank nails. The NDS asks for 6D for nails and wood screws and 4D for lag screws, measured into the main member and excluding the tapered tip on a lag screw.
Can I nail into end grain?
Not for a loaded connection. Eurocode 5 clause 8.3.1.2(3) states that nails in end grain shall not be considered capable of transmitting lateral forces. A narrow exception allows one third of the capacity for non-smooth nails with at least three per connection and 10d penetration, but if a joint depends on it, redesign the joint.
Why do Eurocode 5 and the NDS give different answers?
Because they are built differently. Eurocode 5 gives formulas for every fastener type. The NDS gives tables only for bolts, lag screws and drift pins, and for nails and wood screws requires only that spacing prevents splitting. For a 5 mm (0.2 in) nail along the grain Eurocode 5 demands 75 mm (3 in) to the loaded end and the NDS demands nothing at all. Use the one your jurisdiction has adopted; do not average them.
Does this tell me if my connection is strong enough?
No. It returns minimum geometry against splitting. Whether the joint carries the load needs the fastener capacity, the number of shear planes, member sizes, load duration and service class. Anything structural needs a qualified engineer, and your National Annex or locally adopted edition governs over anything here.