Brick & Block Calculator
Whether you are building a half-brick garden wall, a double-leaf cavity wall or a run of blockwork, getting the quantities right avoids a second delivery charge and a pile of leftover units you have to dispose of.
This calculator turns each wall's area into a brick or block count, then derives the mortar you need to lay them — and splits that mortar into cement bags and sand by weight, volume or bag count. Every constant it uses (joint thickness, waste, mortar mix, bulking, cement and sand density, bag yield) is visible and adjustable, and a cross-check table shows the resulting mortar per square metre beside published reference figures so you can sanity-check the answer.
Add as many walls as your project needs, deduct doors and windows, pick a unit-size preset or enter a custom size, and the results panel updates in real time. Switch between metric and imperial at any point; the calculation runs entirely in your browser.
How to use the brick & block calculator
Start by choosing metric or imperial units at the top. The calculator remembers your preference in your browser.
Open the Assumptions & materials card to pick a unit-size preset. The joint, waste, leaf and mortar defaults fill in automatically for that unit type, but you can override any of them — or choose Custom size and enter your own unit length, width and height.
Add a wall for each distinct run: enter its length and height (or switch that wall to Area entry if you already know the square metres), pick the leaf, and add any door or window openings to deduct. Each wall shows its own gross and net area, unit count and mortar; the Results panel accumulates every wall into project totals plus a cement and sand shopping list.
How to estimate bricks, blocks and mortar in 5 steps
- Choose unitsSelect metric (mm, m, m³, kg) or imperial (in, ft, yd³, lb) at the top of the page.
- Pick a unit sizeOpen Assumptions & materials and choose a preset — UK brick, concrete or aircrete block, US modular brick — or select Custom and enter the unit length, width and height.
- Add walls and openingsAdd one wall per run. Enter its length and height (or a known area), pick the leaf, and add any door or window openings to deduct from the net area.
- Set joint, waste and mixAdjust the mortar joint, waste percentage, mortar mix ratio and cement bag weight. The defaults suit the chosen unit type but can all be overridden.
- Read the resultsThe results panel shows the units to buy, wet mortar volume, cement bags and sand — toggle sand between weight, volume and bags — plus an optional material cost per square metre.
How the brick and block count is worked out
The count starts from the coordinating footprint of a single unit — its work size plus one mortar joint on the length and the height. For a UK metric brick (215 × 65 mm face) with a 10 mm joint, that footprint is 225 × 75 mm, so one square metre holds 1 ÷ (0.225 × 0.075) ≈ 59.3, rounded to the familiar 60 bricks per m² for a half-brick (single-leaf) wall.
A one-brick (double-leaf) wall is two skins, so the figure doubles to about 120 bricks per m². A standard concrete or aircrete block has a 440 × 215 mm face; with a 10 mm joint the coordinating face is 450 × 225 mm, giving 1 ÷ (0.45 × 0.225) ≈ 9.9, rounded to 10 blocks per m² for every block thickness.
The final purchase count is netArea × unitsPerM2 × leafFactor × (1 + waste), rounded up to whole units. Net area is the gross wall area minus the area of any openings you add, so doors and windows are deducted before the count — and an opening larger than the wall, or openings that meet or exceed the wall area, are flagged rather than silently clamped.
How the mortar, cement and sand are worked out
Rather than hiding a single mortar-per-m² number, the calculator derives the wet mortar from the joint geometry: for each unit it is [(workLength × joint) + (workHeight × joint)] × leaf depth. A mortar-waste allowance is then added — small for brick, larger for block — because published block figures embed generous perp-filling and site wastage that pure joint geometry under-predicts. The allowance is shown and adjustable in the assumptions card.
The wet volume is multiplied by a bulking factor (1.30 by default) to give the dry volume, which is split by the mortar mix ratio. For a 1:n cement-to-sand mix the cement volume is dry ÷ (1 + n) and the sand volume is dry × n ÷ (1 + n). Cement volume is converted to bags by dividing by the bag yield (0.0347 m³ for a 50 kg bag, 0.0174 m³ for 25 kg) and rounded up; sand volume is converted to weight with a bulk density of 1600 kg/m³.
The table below shows the mortar per square metre this method produces at the default settings beside widely-published reference figures, so you can confirm your overrides still land in a sensible range.
| Wall type | Computed (m³/m²) | Published (m³/m²) |
|---|---|---|
| Half-brick (UK brick, single leaf) | 0.019 | 0.02 |
| One-brick (UK brick, double leaf) | 0.039 | 0.04 |
| Concrete block 100 mm | 0.012 | 0.012 |
| Concrete block 140 mm | 0.017 | 0.017 |
| Concrete block 215 mm | 0.024 | 0.024 |
Unit size reference
The presets below carry standard work sizes and the resulting units per square metre at a 10 mm joint. Choose Custom size to enter any other unit — the count and mortar recompute from your dimensions.
US modular brick uses a ⅜ inch (about 9.5 mm) joint and is a `likely` figure drawn from secondary sources; confirm against your supplier before ordering.
| Unit | Work size | Units per m² |
|---|---|---|
| UK metric brick — half-brick | 215 × 102.5 × 65 mm | 60 |
| UK metric brick — one-brick | 215 × 102.5 × 65 mm | 120 |
| Concrete block 100 mm | 440 × 215 × 100 mm | 10 |
| Concrete block 140 mm | 440 × 215 × 140 mm | 10 |
| Concrete block 215 mm | 440 × 215 × 215 mm | 10 |
| Aircrete block | 440 × 215 mm face | 10 |
| US modular brick | 194 × 92 × 57 mm | ≈ 74 |
Frequently asked questions
How many bricks are there per square metre?
A half-brick (single-leaf) wall of standard UK metric bricks needs about 60 bricks per square metre, derived from the 225 × 75 mm coordinating size at a 10 mm joint. A one-brick (double-leaf) wall is two skins, so it needs about 120 bricks per square metre. The calculator applies your chosen joint and waste, so the figures adjust if you change them.
How many concrete blocks are there per square metre?
A standard concrete or aircrete block has a 440 × 215 mm face. With a 10 mm joint the coordinating face is 450 × 225 mm, giving about 10 blocks per square metre — and that is true for every block thickness (100, 140 and 215 mm) because they share the same face size. Only the wall thickness and mortar volume change with block thickness.
What is the difference between a single-leaf and double-leaf wall?
A single leaf is one unit thick — a half-brick wall (102.5 mm) or a single block. A double leaf, or one-brick wall (215 mm), is two brick skins bonded together, as in English or Flemish bond. Doubling the leaf roughly doubles both the brick count and the mortar, which is why the leaf control moves a brick wall between about 60 and 120 bricks per square metre.
How much mortar do I need per square metre?
A half-brick wall uses roughly 0.02 m³ of mortar per square metre and a one-brick wall about 0.04 m³. Blockwork uses about 0.012 m³ per m² at 100 mm, 0.017 at 140 mm and 0.024 at 215 mm. The calculator derives these from the joint geometry plus an adjustable mortar-waste allowance and shows the computed figure beside these published values so you can cross-check.
How much cement and sand does the mortar need?
The wet mortar is bulked to a dry volume (×1.30 by default) and split by the mortar mix ratio: for a 1:n cement-to-sand mix the cement is 1 ÷ (1 + n) of the dry volume and the sand is n ÷ (1 + n). Cement volume is converted to bags using the bag yield (0.0347 m³ per 50 kg bag) and rounded up; sand volume is converted to weight at 1600 kg/m³. You can read sand as weight, volume or bags in the results panel.
How do I deduct doors and windows?
Add an opening to a wall with its width, height and count, and its area is subtracted from the gross wall area before the count and mortar are worked out. The wall row shows both the gross and net area. If an opening is larger than the wall, or the openings meet or exceed the wall area, the calculator flags it rather than returning a nonsensical negative count.
What mortar mix ratio should I use?
Common bricklaying mixes run from 1:3 (strong, for engineering brick and below-DPC work) to 1:6 (softer, for general and internal blockwork), with 1:4 and 1:5 the everyday choices. A stronger mix uses more cement and less sand per cubic metre. Pick the ratio in the assumptions card and the cement bag and sand quantities update accordingly.
Does the calculator work in metric and imperial?
Both. Switch units at the top and every dimension and result converts: unit sizes in mm or inches, walls in m or ft, mortar in m³ or yd³, and sand in kg and tonnes or pounds and short tons. The calculation is done in SI internally and only converted for display, so switching units never changes the underlying answer.
Is the calculator private?
Yes. Every calculation runs entirely in your browser. Nothing you enter is sent to any server, and your project is saved only in your own browser's local storage.