The perpend gauge is the width of one brick (the header) plus the width of one cross joint. It is the base dimension a bricklayer uses to set out a wall along its length, so that the perpends line up course after course.
The rule behind good brickwork
For a bond to work out visually, the length of a brick (the stretcher) equals twice its width (the header) plus one cross joint.
For the Dutch waal format (roughly 210 x 100 x 50 mm) that works out exactly:
- header 100 mm + cross joint 10 mm = perpend gauge 110 mm
- 2 x 100 + 10 = 210 mm = the stretcher length
The same logic applies to the standard UK brick of 215 x 102.5 x 65 mm with a 10 mm joint: 2 x 102.5 + 10 = 215 mm, giving a perpend gauge of 112.5 mm. The customary joint width therefore follows from the brick size — it is not an arbitrary figure.
| Dutch waal format | Roughly 210 x 100 x 50 mm; header 100 mm + cross joint 10 mm = perpend gauge 110 mm; stretcher 210 mm |
|---|---|
| Standard UK brick | 215 x 102.5 x 65 mm; header 102.5 mm + joint 10 mm = perpend gauge 112.5 mm; stretcher 215 mm |
Working out the perpend gauge
Bricks are fired products and always vary in size. So do not measure one brick, measure a run:
- Lay 10 stretchers tight against one another and measure the total length.
- Lay 20 headers tight against one another above them and measure that length.
- The difference between the two rows equals exactly 10 cross joints.
- Add that difference to the length of the 20 headers and divide by 20: that is the average perpend gauge.
Mark that dimension out on a perpend gauge rod.
Why it matters
- Avoiding cut bricks — convert wall lengths, piers and opening widths into whole perpend gauges. That way you barely need to cut and the bond stays intact.
- The bond works out — in stretcher, English and Flemish bond, the perpend gauge is the unit in which the pattern repeats. Depart from it and the perpends start to wander.
- Different formats, different gauge — every brick format has its own perpend gauge. Always check against the batch you are laying.
- Thin-joint mortar changes everything — there the joint is about 3 to 5 mm rather than 10 mm. The perpend gauge shrinks accordingly, and the units must be sized to match.
Related terms
- Perpend gauge rod
- Perpend
- Brick sizes
- Bond pattern
- Bricklaying
- Queen closer
Want to know more about construction terms? Visit our knowledge base at fredsdiyplans.com.