Brick Opening Deduction Calculator

The opening deduction method

Calculate the gross wall area first. Then calculate the area of each opening and multiply it by its quantity.

Worked example

A 12 m × 3 m wall has 36 m² gross area. One 0.9 × 2.1 m door removes 1.89 m². Four 1.2 × 1.2 m windows remove 5.76 m². Net brickwork area is therefore 28.35 m² before any other opening or waste allowance.

Why opening shape matters

This calculator models rectangular openings. Arched, circular, stepped or irregular openings need a different area method. A complex façade can also require extra bricks around reveals and returns even though the opening area is correctly deducted.

Waste after deductions

The waste allowance is applied after calculating the net brick quantity. Keeping the order of operations visible prevents accidentally applying waste to a gross wall area that already includes material removed by openings.

Common mistakes

Deducting an opening twice: keep one opening schedule.

Using gross area for ordering: deduct openings first.

Ignoring reveals: opening area alone does not quantify all masonry around the opening.

Using different units: all dimensions must use one unit basis.

Limitations

This tool performs rectangular area deductions and a simple brick-module conversion. It is not a full wall-by-wall masonry takeoff.

Frequently Asked Questions

How do you deduct doors from brickwork?

Multiply door width by height and subtract the total door area from wall area.

Can I deduct multiple windows?

Yes.

Should waste be added after deductions?

Yes, for a clear takeoff sequence.

Does this include lintels?

No.

Can I use irregular openings?

Not directly; calculate their actual area separately first.