Mortar Calculator
Calculate exactly how many bricks or blocks you need and how much builders sand and Portland cement to mix for your brickwork or blockwork. Choose your brick type, mix ratio and wall dimensions for instant results.
Cement Bag Size
Select the size your supplier sells.
Metric Bags
In Australia, cement is sold as GP cement (General Purpose) under AS 3972 — this is the local equivalent of Portland cement.
Default: 94 lb (imperial) · 20 kg (metric)
Brick / block type
Standard UK and Australian clay facing or common brick, 10 mm mortar joints
Mix ratio (cement : sand)
Standard — external facing brickwork
How to Use This Mortar Calculator
- Select your unit system — Metric or Imperial.
- Choose your brick or block type from the list — size and mortar rate are set automatically.
- Enter the wall length and height.
- For brick walls, choose single or double skin.
- Select your mix ratio — 1:5 is standard for most external facing brickwork.
- Results show brick/block count, mortar volume, cement bags and builders sand with a 5% brick waste and 10% material waste allowance.
Mortar Mix Ratios Explained
Mortar is a mix of Portland cement, builders (soft) sand and water. The ratio is expressed as cement : sand by volume:
- 1:3 — High strength. For engineering bricks, below the damp-proof course, or persistently wet conditions. Too strong for most general brickwork.
- 1:4 — Medium strength. General internal brickwork and blockwork.
- 1:5 — Standard. External facing brickwork, chimneys, garden walls.
- 1:6 — Weak. Thermalite, aerated concrete blocks, low-load partitions. Do not use for structural work in exposed locations.
The dry factor of 1.3 is applied because dry materials compact when mixed — approximately 1.3 m³ of dry sand and cement produces 1 m³ of finished mortar.
Brick and Block Coverage Reference
Coverage figures assume 10 mm mortar joints. Add 5% to all counts for cutting and waste.
What Sand to Use for Mortar
Brickwork mortar must use builders sand (also called soft sand). Builders sand has fine, rounded particles that produce a smooth, workable paste that bonds well to brick and stone surfaces.
Do not use sharp sand or concrete sand. These have coarse, angular particles that make mortar harsh and unworkable, reduce adhesion, and can cause the mortar to pull away from the brick face. Sharp sand is correct for screed and concrete — not mortar.
Builders sand is known by different names internationally:
- UK: builders sand, soft sand, yellow sand
- Australia/NZ: brickies sand, plasterers sand
- US: masonry sand, brick sand
- South Africa: plaster sand, building sand
Frequently Asked Questions
What mix ratio should I use for brickwork mortar? +
For most external facing brickwork, a 1:5 (cement:sand) mix is standard — it provides adequate strength while remaining slightly flexible to accommodate movement. Use 1:4 for general internal walls. Use 1:3 only for engineering bricks, below the damp-proof course, or in persistently wet conditions. Thermalite and aircrete blocks always require a weak mix (1:6 or weaker) — strong mortar will crack the block face.
How much mortar do I need per 1,000 bricks? +
As a rule of thumb, allow approximately 1 m³ of wet mortar per 1,000 standard bricks (215×102.5×65 mm) at 10 mm joints. This accounts for bed joints, perpend joints and normal waste. The actual quantity varies with brick size and joint thickness — use the calculator for precise figures.
What is the difference between builders sand and sharp sand for mortar? +
Builders sand (also called soft sand or brickies sand in Australia) has fine, rounded particles that produce a smooth, workable mortar with good adhesion to brick faces. Sharp sand (concrete sand) has coarse, angular particles — it makes mortar harsh, difficult to trowel, and weakens the bond with the brick. Always use builders sand for brickwork mortar. Never substitute sharp sand.
Why does thermalite need a weak mortar mix? +
Thermalite (autoclaved aerated concrete / AAC) is a very soft, low-density block. Standard Portland cement mortar (1:3 to 1:5) is far stronger and more rigid than the block itself. When the wall moves with temperature or loading, the rigid mortar joint cannot flex — stress concentrates in the block and causes spalling and cracking along the joint. Use a 1:6 mix or proprietary thin-bed adhesive mortar designed for AAC blocks.
How long does mortar take to set and cure? +
Mortar reaches initial set in 1–2 hours under normal conditions (15–20 °C). It is firm enough to build on after 24 hours. Full cure takes 28 days. Do not point or load the wall heavily for at least 24 hours. Protect fresh mortar from frost (below 2 °C) and from drying too quickly in direct sun or wind — both conditions weaken the final joint.
What is the difference between a single and double skin wall? +
A single skin (half-brick) wall is one brick wide — approximately 102.5 mm thick for standard UK bricks. It uses one layer of bricks laid as stretchers. A double skin (full-brick) wall is one full brick wide — approximately 215 mm thick — with bricks laid as headers, or two skins with a cavity. Double skin walls use roughly twice the bricks and mortar. Most cavity walls are built as two single skins with a 50–100 mm air or insulated cavity between them.
Can I use pre-mixed bagged mortar instead of mixing my own? +
Yes — pre-mixed dry mortar (cement and sand already combined, just add water) is convenient for small jobs. It costs more per tonne than mixing from scratch but saves labour and reduces waste on small repairs. Check the bag for the mix ratio — most are formulated as 1:4 or 1:5. For large projects, site-batched mortar from bulk materials is significantly cheaper.
What is pointing mortar and is it different from bedding mortar? +
Bedding mortar is the full mortar joint laid as each course is built — it carries the structural load between bricks. Pointing mortar is applied to the exposed face of a joint, either to finish new brickwork or to repoint old joints that have weathered and eroded. Pointing mixes are typically slightly richer (1:4 to 1:5) for better weather resistance. Repointing old brickwork: always match the original mortar strength — using modern hard mortar on soft old bricks will cause the bricks to crack.