Pattern — | hole — | suggested min edge — in, min spacing — in
Hole Pattern Summary
- Pattern—
- Bolt / hole—
- Center spacing—
- Edge distance—
- Overall size—
Minimum Bolt Spacing
| Bolt size | Typical min spacing | Min edge distance |
|---|---|---|
| 3/8 in | 1.5 in | 0.6 in |
| 1/2 in | 2 in | 0.75 in |
| 5/8 in | 2.5 in | 1 in |
| 3/4 in | 3 in | 1.25 in |
| 1 in | 4 in | 1.75 in |
Minimum spacing is about 3x bolt diameter; minimum edge distance about 1.5x to 2x diameter. Codes set the governing values.
How Far Apart Should Bolts Be?
Bolt spacing balances two limits: bolts must be far enough apart to install and to avoid tearing the material between them, and far enough from the edge to avoid pulling out the side. A common rule of thumb puts minimum center-to-center spacing at about three bolt diameters and minimum edge distance at roughly one and a half to two diameters, with the governing code setting the real numbers. This calculator turns a pattern, a bolt size, and a spacing into a bolt count, edge distance, overall size, and a scaled drawing of where the holes go.
Bolt Patterns: Linear, Rectangular, and Circular
Most layouts are one of a few shapes. A linear pattern is a single row, common in wood splices and steel splice plates. A rectangular or square grid is the workhorse for base plates and equipment mounts. A circular bolt pattern, often called a bolt circle, places bolts evenly around a diameter and is standard for flanges and round equipment. For a bolt circle, the spacing between neighbors is a chord of the circle, which this calculator computes from the bolt circle diameter and the number of bolts.
Edge Distance and Hole Size
Edge distance is measured from the bolt center to the nearest edge, and skimping on it is the most common layout mistake. Hole size matters too: a standard clearance hole is about one sixteenth of an inch larger than the bolt, oversized and slotted holes give erection tolerance but need plate washers and can reduce capacity. Match the hole type to how much field adjustment the connection needs, and keep edge distance measured to the hole, not the bolt, when holes are large.
Frequently Asked Questions
How far apart should bolts be? About three bolt diameters center to center as a minimum, more for clearance and load.
Minimum edge distance? Roughly 1.5 to 2 bolt diameters from center to edge, per code.
Bolt spacing for base plates? Set by the column and bolt size; four bolts in a rectangle clear of the flange is typical.
What is a bolt circle? Bolts spaced evenly around a circle of a given diameter, used for flanges and round parts.