Brick & Block Calculator

How this calculator works

You don’t have to do any of this maths yourself - the calculator handles every step. This is just what is going on behind the scenes, in case you like to know.

A brick or block wall is measured like any wall: first work out the gross wall area (each wall’s length times its height), then take off the doors and windows to leave the net area - the part you actually cover in brick. The rest is turning that net area into a number of bricks, plus the mortar and the sand:

units per area = 1 ÷ ((unitL + joint) × (unitH + joint))   (one wythe)
gross area     = sum of (wall length × wall height)
net area       = gross − (door & window areas)
units          = ceil( net area × units/area × wythes × wastage )
mortar volume  = net units × unit depth × (cell − unit face) × wastage   (full-bed)
sand (mixing)  ≈ mortar volume      mortar mix bags = ceil( mortar volume ÷ bag yield )

Every brick takes up its own size plus one mortar joint on two sides - a joint on top (the bed joint) and a joint to one side (the head joint). So the space one brick really fills is (brick length + joint) × (brick height + joint), and the number of bricks per square metre (or per square foot) is one divided by that space. A double-wythe wall - two layers of brick thick, also called two leaves or two skins - lays two bricks for every spot on the wall, so it needs twice the bricks and twice the mortar. The mortar fills the gaps around every brick; this is a generous (full-bed) estimate, so hollow blocks - which are only buttered with mortar around the edges - use a little less. If you mix your own mortar on site, the sand you need is about the same as the finished mortar volume, so the sand figure follows the mortar; if you buy ready-mixed bags instead, the calculator tells you how many bags to get.

Worked example

This example follows the unit system you pick in the calculator above.

An 8 m × 2.4 m single-leaf (one brick thick) wall in 215 × 65 mm brick, minus one 1.2 m × 1.2 m window, 5% waste:

1. Gross wall area: 8 × 2.4 = 19.2 m².
2. Deduct the window: 1.2 × 1.2 = 1.44 m², so net = 17.76 m².
3. Units per m²: 1 ÷ (0.225 × 0.075) = 59.3 bricks/m² (face plus a 10 mm joint each way).
4. Add 5% waste: ceil(17.76 × 59.3 × 1.05) = 1,106 bricks.
5. Mortar: about 0.33 m³ - so roughly 24 bags of mortar mix, or about 0.33 m³ of sand if you mix your own.

Bricks and blocks per area, by unit size

The unit size and the joint set the per-area count - that is what turns a wall area into a number to buy. These are the common units laid to a 10 mm (3/8 in) joint:

A double-skin wall needs twice these figures. The mortar grows with the joint and the unit depth, so a thick block bed uses more mortar per unit than a thin brick joint even though the block count is far lower.

Curved walls and round fire pits

Brickwork on a curve is counted the same way as a straight wall - you just measure the length along the curve itself (its running, or developed, length) instead of in a straight line. Set a wall’s shape to Curved and enter the diameter (the width measured across the middle of the wall) and the sweep angle (how far around the circle the wall goes - a quarter turn is 90°, a half is 180°); the run is π × diameter × angle ÷ 360. A round fire pit or fireplace is a full circle, so switch the shape to Round and the run becomes the whole circumference, π × diameter. The brick count, the mortar and any opening you deduct all follow from that area, exactly as for a straight wall.

Because rectangular bricks wedge on a curve - the joints open on the outside and you cut more on a tight radius - add a little more waste the tighter the curve. The count here is the structural ring only; line the inside of a fire pit with fire brick set in refractory mortar. For the ring-by-ring method and a table by pit diameter, see how many bricks for a fire pit.

Tips for measuring and ordering brick

• Measure each wall length times height, then take off the doors and windows so you are not paying to lay brick over them. The calculator works out each wall on its own, so a big opening on one wall never eats into another.
• Pick the preset that matches your brick or block, or type the unit’s actual face and depth and the joint - the per-area count and the mortar both come off those numbers.
• Set single or double wythe (one or two layers of brick thick) to match your wall. A brick veneer - a single skin of brick in front of a timber or block wall - is single; a solid two-layer wall is double. A cavity wall - two walls with a gap between them - is usually the outer brick layer plus a separate run of the block calculator for the inner layer.
• Buy the mortar whichever way the result shows it: ready-mixed bags by the count, or that volume of sand plus masonry cement if you are mixing your own. Round the mortar up - it is cheap compared with running out partway up the wall.
• Order a little long and keep the batch / lot number; clay and concrete units can vary slightly in shade between runs.
• For the footing or slab the wall sits on, the concrete calculator works out the concrete, the concrete mix calculator gives the cement, sand and gravel if you are mixing it, and the paver calculator handles a paved area in the same masonry family.
• For the full method and worked figures, see how many bricks do I need, the per-area figures in how many bricks per square foot, the standard brick sizes, and the mortar in how much mortar do I need. Laying brick flat for a patio or building a fire pit? Those have their own guides.

Standard brick and block sizes where you are

In New Zealand, the brick most jobs use is a clay brick for veneer, with sizes varying by maker - enter your brick's actual face and depth in the calculator, and the concrete equivalent is a concrete masonry block, with 390 × 190 × 190 mm the standard size that clads and builds most block walls. Masonry is laid to a 10 mm joint, which sets the per-area count off the unit size. Enter your unit's actual face and depth, plus the joint, in the calculator above - or pick the matching preset - so the per-area count and the mortar come out right for the unit you are actually buying.

For the recognised specification and laying detail, see AS/NZS 4455 (Masonry Units) and NZS 4210 (Masonry Construction: Materials and Workmanship).