How far from the end of a board can a bolt go?

Seven diameters where the joint is in tension, four where it is in compression — so 3 1/2" and 2" respectively for a 1/2" bolt. The asymmetry is the most useful thing here: a tension joint is trying to split a plug of wood out of the end of the board, and compression is not, so turning a connection around so the wood is pushed rather than pulled nearly halves the end distance it needs.

Why is everything measured in bolt diameters?

Because the wood around the hole is the structure, not the bolt. A 1/2" bolt concentrates its load over twice the area a 1/4" one does and needs twice the wood around it to spread that into, so every minimum scales with the fastener. It is the same reason the numbers do not change when you move to a bigger timber — a wider board does not make a bolt near its end any safer.

Are these numbers the building code?

They are the NDS geometry requirements for full design value, which is the standard the code references rather than the code itself — so treat them as defaults, not law. They are also only the geometry: they say a connection is spaced so the wood can develop its capacity, and say nothing about whether that capacity carries your load. A connection holding a structure up gets designed, and ring the building department for what your jurisdiction has adopted.

How much bigger than the bolt should the hole be?

A sixteenth, or a thirty-second if the pieces are drilled together. Enough that the bolt goes through two parts whose holes never line up perfectly, and no more — the slop is movement before the joint takes any load at all, and on a connection that gets cycled that movement works the hole oval. A lag screw is different and is not this number: its threads cut their own way and it needs a pilot hole smaller than its shank.

Bolt and lag spacing in timber

A bolt through a beam does not fail because the bolt was too small — it fails because the wood between it and the end of the board split out. These are the distances that stop that, measured in bolt diameters, with true-size drill templates below.

Bolt diameter

Member width

Across the grain

Wood past the joint

Along the grain, from the joint line to the end of the board

Bolts per row

Rows

What the joint does to the wood

A tension joint tries to split a plug out of the end, so it needs far more room

Minimums for a 1/2" bolt

End (7D)

3 1/2"

Edge (1.5D)

3/4"

Between bolts (4D)

Between rows (1.5D)

3/4"

Drill the hole

9/16"

Does this pattern fit the timber

All 2 checks passShow the numbers

2 rows fits the width — passesNeeds 2.25" across the grain; the member is 5.5".
2 bolts per row clears the end — passesNeeds 5.5" from the end; there is 12".

Width the pattern needs: 2 1/4"
Length past the joint it needs: 5 1/2"
Most bolts per row that fit: 5
Most rows that fit: 6
Bolts in total: 4

Drill templates, at true size

Two strips rather than one grid — row position across the width, bolt position along the length — so each one fits the timber it's held against. Print at 100%, check the ruler, then hold each strip flush to its own reference edge.

Check this first

Put a tape on the printed ruler. If it does not read exactly 6 inches, the print was scaled — set the print dialog to 100% or “Actual size” and print it again. Do not cut wood from a template that failed this.

Row position, across the width

Hold flush against one long edge of the timber. Each tick is a row's centerline.

Bolt position, along the length

Hold flush against the end of the board. Each tick is one bolt's centerline, in a single row.

Turn the joint around

End distance is 7D where the joint pulls the board apart and only 4D where it pushes — 3 1/2" against 2" for this bolt. Arranging a connection so the wood is in compression is the cheapest way there is to buy back room at the end of a board.

Defaults, not law

These are the NDS geometry requirements for full design value — the standard the building code references rather than the code itself. They say the wood around the hole is spaced to develop its capacity; they say nothing about whether that capacity carries your load. Reduced spacings are permitted at a reduced design value and are deliberately not offered here, because that is a decision with a load behind it.

Ring the building department for what your jurisdiction has adopted, and get anything holding a structure up designed by somebody who will stamp it.

Worked example: four 1/2" bolts

Four 1/2" bolts — two rows of two — through a 5 1/2" member pulling apart need 3 1/2" of end distance (7D), 3/4" to each edge (1.5D), 2" between bolts (4D) and 3/4" between rows (1.5D), in 9/16" holes.

The pattern needs 2 1/4" of width and 5 1/2" of wood past the joint. It passes both of the NDS geometry checks the calculator applies.

These are the NDS spacings for full design value. They say nothing about whether the connection carries your load; that is for the building department and an engineer.

End (7D): 3 1/2"
Edge (1.5D): 3/4"
Between bolts (4D): 2"
Between rows (1.5D): 3/4"
Drill the hole: 9/16"

These are the figures the calculator above opens on. Change any field and it works the same problem for your numbers.

About bolting into timber

How far from the end of a board can a bolt go?: Seven diameters where the joint is in tension, four where it is in compression — so 3 1/2" and 2" respectively for a 1/2" bolt. The asymmetry is the most useful thing here: a tension joint is trying to split a plug of wood out of the end of the board, and compression is not, so turning a connection around so the wood is pushed rather than pulled nearly halves the end distance it needs.
Why is everything measured in bolt diameters?: Because the wood around the hole is the structure, not the bolt. A 1/2" bolt concentrates its load over twice the area a 1/4" one does and needs twice the wood around it to spread that into, so every minimum scales with the fastener. It is the same reason the numbers do not change when you move to a bigger timber — a wider board does not make a bolt near its end any safer.
Are these numbers the building code?: They are the NDS geometry requirements for full design value, which is the standard the code references rather than the code itself — so treat them as defaults, not law. They are also only the geometry: they say a connection is spaced so the wood can develop its capacity, and say nothing about whether that capacity carries your load. A connection holding a structure up gets designed, and ring the building department for what your jurisdiction has adopted.
How much bigger than the bolt should the hole be?: A sixteenth, or a thirty-second if the pieces are drilled together. Enough that the bolt goes through two parts whose holes never line up perfectly, and no more — the slop is movement before the joint takes any load at all, and on a connection that gets cycled that movement works the hole oval. A lag screw is different and is not this number: its threads cut their own way and it needs a pilot hole smaller than its shank.