Bed joint needed for a target

This finds the average bed joint you would need to make a chosen number of courses reach a target height exactly. Use it to see whether a height can be gauged out by adjusting the beds.

H is the target height in mm. n is the number of courses and h is the height of one unit, so n × h is the height taken up by the units alone. n_b is the number of bed joints you are counting within that height. j_b is the average thickness each bed must be.

Whatever height the units do not fill must be taken up by mortar, so the remaining space, H − nh, is shared equally between the beds. The bed count is entered separately because it depends on your datum convention.

For 32 courses of 65 mm bricks to reach 2400 mm, the units take 2080 mm, leaving 320 mm over 32 beds: exactly 10 mm each.

Watch out: getting a number does not mean the joint is acceptable. Check it against the mortar specification and tolerances.