Brick and Block Mortar Calculator
Estimate how many bricks or blocks a wall needs and how much wet mortar goes into the joints, then the cement and building sand for a site mix or the number of pre-bagged mortar bags.
Results
Enter your project measurements to see your results.
What the mortar calculator does
It works out the wall area left after doors and windows, how many units fit on that area with your joint sizes, and how much wet mortar fills the joints. Breakage is added to the unit count and waste to the mortar, each once and separately, before the mortar is turned into cement and sand or bags.
How to measure a wall
- Measure the length along the base and the height to the top course.
- For gable ends or stepped walls, split the face into rectangles and enter the total area.
- Measure each door, window and vent opening and add it to the openings list.
- Treat each wall separately where the unit or build changes.
How unit size and joints change the numbers
Each unit takes up its own face plus one bed joint and one perpend joint. A 215 × 65 mm brick with 10 mm joints therefore occupies 225 × 75 mm, which is why one square metre holds about 59 bricks. Larger blocks cover more area each, so far fewer are needed. Thicker joints reduce the unit count slightly but increase mortar noticeably, because the joint volume grows with both the thickness and the bed depth.
Single-skin and double-skin walls
A single skin is one unit thick, laid in stretcher bond. A double skin here means two stretcher-bonded skins side by side, with an optional mortar-filled collar joint between them. Each skin has its own bed and perpend joints, and the collar joint is added once across the wall area. For a cavity wall, enter 0 for the collar joint; if the two leaves use different units, calculate each leaf separately as a single skin.
Limitations: the calculator does not model header bonds such as English or Flemish bond, piers, corners and returns, frogged or perforated units filled with mortar, curved walls or decorative patterns. For those, the result is only a rough guide — ask your supplier or bricklayer for a quantity.
Building sand and sharp sand
Building sand (soft sand) is fine and well graded, which makes a workable, smooth mortar for laying bricks and blocks. Sharp sand is coarser and angular, used in screeds, concrete and paving beds. The sand density here is an editable estimate; damp sand weighs more and bulks up.
Site-mixed or pre-bagged mortar
A site mix is batched from cement and building sand by volume, sometimes with lime or a plasticiser. Its yield depends on how the materials pack and how much water is used, so the calculator uses a dry volume factor you can change. Pre-bagged mortars are factory blended and the manufacturer states a yield; the calculator uses only the yield you enter.
Worked metric example
A 5 m × 2 m single-skin wall of UK standard bricks with a 0.9 × 2.1 m door has a net area of 8.11 m². At 10 mm joints that is about 481 bricks, or 505 with 5% breakage. Mortar is about 0.143 m³, or 0.157 m³ with 10% waste. With a 1:5 mix, a 1.3 dry volume factor and the starting densities, that is roughly 49 kg of cement (2 bags of 25 kg) and 272 kg of building sand.
Worked imperial example
A 20 ft × 6 ft wall of 15 5/8 × 7 5/8 × 7 5/8 in blocks with 3/8 in joints is 120 sq ft. Each block occupies 16 × 8 in, so the wall needs 135 blocks before breakage, with about 0.2 yd³ (5.3 ft³) of mortar before waste. That assumes full mortar beds; hollow blocks laid on face shells only use less.
Structural and exposure requirements
The calculator estimates quantities only. Mortar designation, wall ties, damp-proof courses, movement joints, foundations and load-bearing or exposure performance depend on the design, the units and local building regulations. Get advice from a structural engineer, building control or a qualified builder. For foundations, try the concrete calculator trench option, and for a base under a garden wall or shed, the shed base calculator.
Frequently asked questions
- How much mortar do I need per square metre of brickwork?
- For UK standard bricks (215 × 65 × 102.5 mm) laid in a single skin with 10 mm joints, the geometry gives about 59 bricks and 0.018 m³ of wet mortar per m², before waste. Thicker joints, frogged bricks or deeper beds change that figure, so use your own sizes.
- How many blocks are in a square metre?
- A 440 × 215 mm block face with 10 mm joints occupies 450 × 225 mm, so one skin needs about 9.9 blocks per m² before breakage.
- Does a 1:5 mortar mix give a known yield?
- No. A ratio describes proportions of loose cement and sand by volume. The materials shrink in volume when mixed with water, so the calculator multiplies the wet volume by an editable dry volume factor. Treat the cement and sand figures as estimates.
- Should I use building sand or sharp sand for mortar?
- Bricklaying mortar is usually made with soft building sand, which is finer and more workable. Sharp sand is coarser and is used for screeds, concrete and paving beds. Follow the specification for your project.
- How does a double-skin wall change the estimate?
- The calculator treats it as two stretcher-bonded skins, each with its own joints, plus an optional mortar-filled collar joint between them. It does not simply double the result unless that is what the geometry gives, and it does not model header bonds.
- Can this tell me which mortar strength or wall design to use?
- No. Mortar designation, wall ties, movement joints and load-bearing or exposure requirements depend on the design and local regulations. Ask a structural engineer, building control or a qualified builder.