Material estimator · Fixings
Timber fastener spacing
How far apart fixings go in timber, how far from the end and the edge, and why the answer is a multiple of the fastener rather than a number in millimetres.
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Why there is no single number
People search for a spacing in millimetres and there is not one, because the rule is proportional. Spacing is expressed as a multiple of the fastener diameter — so a thicker screw needs more room in every direction, and the same “rule” produces a different distance for every fixing you pick up.
There is also not one distance but several, and they are different from each other:
| Distance | What it is, and what it protects against |
|---|---|
| Along the grain | Spacing between fixings in a line running with the grain. Too tight and the line becomes a split waiting to happen. |
| Across the grain | Spacing between parallel lines of fixings. Smaller than the along-grain figure, because timber splits along the grain and not across it. |
| Loaded end | From the end of the timber on the side the force pulls towards. The largest of the four, and the one most often got wrong. |
| Unloaded end | From the end on the side with no pull. Smaller, because nothing is trying to tear the fibres out. |
| Loaded edge | From the long edge on the loaded side. |
| Unloaded edge | From the long edge on the other side. The smallest of the set. |
The two ways a fixing fails
Too close — to each other, or to an end — and the timber splits along the grain. A split removes exactly the strength the fixing was there to provide, and it usually happens at the moment of driving rather than under load, so it is visible if you look. Too far apart and the joint simply has fewer fixings than the load needs. Spacing rules exist to hold both off at once, which is why they have a minimum and the number of fixings has a separate one.
What changes it
- ·Fastener type — nails and screws do not share multipliers, and a screw in a pre-drilled hole differs again.
- ·Diameter — the multiplier is applied to it, so this is the single most important input.
- ·Pre-drilling — changes what the timber will tolerate before it splits.
- ·Timber density — a hardwood and a softwood do not behave the same.
- ·Which side is loaded — end and edge distances are larger where the force pulls.
Working it out
Enter the fastener and the timber and the calculator returns all six distances together, so you can set out a joint without doing six multiplications and keeping them straight. If you are counting fixings for a whole structure rather than setting out one joint, the 3D build planner counts the joints and derives the fixings from them.
Free, no account, metric or imperial.
Where fixings decide the job
Structures held together by what connects the pieces rather than by the pieces themselves.
Common questions
How far apart should timber screws be?
It depends on the fixing diameter, not on a fixed distance in millimetres. Spacing rules are expressed as multiples of the fastener diameter, with separate figures for spacing along the grain, across it, and from the loaded or unloaded end and edge. The calculator works them out for the diameter and timber you enter.
What is end distance and edge distance?
End distance is how far the fixing sits from the end of the timber, measured along the grain; edge distance is how far it sits from the long edge. End distance is the one that splits timber when it is too small, and it is larger on the loaded side than the unloaded side because that is where the force pulls.
Why does fastener spacing matter?
Two failure modes. Too close together or too near an end and the timber splits along the grain, which removes the strength the fixing was providing. Too far apart and the joint has fewer fixings than it needs for the load. Spacing rules exist to keep both away at once.
Do nails and screws use the same spacing?
No. The multiples differ by fastener type, and screws in pre-drilled timber differ again from screws driven without a pilot hole. Diameter is the input that matters in every case.
Does the timber species change it?
It can. Denser timber splits differently from softwood, and pre-drilling changes the required distances. Spacing is a starting point from the fastener and the timber — for anything structural, the requirement that applies where you are building is the one that counts.