Mortar calculator: cement, sand and per m²
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Work out how much cement and sand, or how many pre-mixed bags, your brickwork or blockwork needs, and the mortar per m² of wall. Enter your measurements below; every figure we start from is shown and you can change it.
Worked example
| You enter | Value |
|---|---|
| Mixing | Cement and sand |
| Number of bricks or blocks | 593 |
| Laying | Bricks |
| Unit length | 215 mm |
| Unit width | 103 mm |
| Unit height | 65 mm |
| Joint | 10 mm |
| Waste allowance | 10% |
| Mix ratio: parts sand to 1 part cement | 4 parts |
| Dry-volume factor | 1.3 × |
| Cement density | 1,440 kg/m³ |
| Building sand density | 1.5 t/m³ |
| Cement bag size | 25 kg |
Order: 3 bags of cement and 0.30 t of sand
| Result | Value |
|---|---|
| Cement bags | 3 |
| Cement | 72.6 kg |
| Building sand | 302.5 kg |
| Wet mortar | 0.194 m³ |
| Dry materials | 0.252 m³ |
| Bricks or blocks per m² of wall (one skin) | 59.26 per m² |
| Wet mortar per m² of wall (before waste) | 17.6 L/m² |
| Cement per m² of wall (before waste) | 6.59 kg/m² |
| Sand per m² of wall (before waste) | 27.5 kg/m² |
Show the working
- Per unit: ((0.215 + 0.01) × (0.065 + 0.01) − 0.215 × 0.065) × 0.103 m = 0.000297 m³
- Wet mortar: 593 × 0.000297 × 1.1 (10% waste) = 0.194 m³
- Per m² of wall: 1 ÷ ((0.215 + 0.01) × (0.065 + 0.01)) = 59.26 units; × 0.000297 m³ = 17.6 L of wet mortar per m²
- Dry volume: 0.194 × 1.3 = 0.252 m³
- Cement: 0.252 ÷ (1 + 4) × 1,440 kg/m³ = 72.6 kg
- Sand: 0.252 × 4 ÷ (1 + 4) × 1.5 t/m³ = 0.3 t
- Per m² of wall: 6.59 kg cement and 27.5 kg sand (no waste)
- Cement bags: 72.6 kg ÷ 25 kg, rounded up = 3
How it works
- Mortar per unit (m³) = ((length + joint) × (height + joint) − length × height) × width. Frogs are ignored.
- Wet mortar = units × mortar per unit × (1 + waste); dry materials = wet × dry-volume factor
- Cement (kg) = dry ÷ (1 + r) × cement density; sand (t) = dry × r ÷ (1 + r) × sand density, for a 1 : r mix
- Pre-mixed bags = wet mortar (L) ÷ the yield printed on the bag, rounded up
- Per m² of wall: units per m² = 1 ÷ ((length + joint) × (height + joint)); mortar per m² = mortar per unit × units per m², split into cement and sand as above (no waste)
The mix ratio depends on the job: check your maker's or builder's spec.
Frogs (the dip in some bricks) are ignored, so laying frog-up uses more.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Unit length: Bricks | 215 mm | Common UK size Not yet checked against the source | From your product UK standard brick (work size). |
| Unit width: Bricks | 102.5 mm | Common UK size Not yet checked against the source | From your product UK standard brick (work size). |
| Unit height: Bricks | 65 mm | Common UK size Not yet checked against the source | From your product UK standard brick (work size). |
| Unit length: Blocks | 440 mm | Common UK size Not yet checked against the source | From your product UK standard block face. |
| Unit width: Blocks | Enter from the bag, pack or tin | Common UK size Not yet checked against the source | From your product brief v2 B1: block thickness (wall width) for block mortar. Not stated in the brief; from the block. |
| Unit height: Blocks | 215 mm | Common UK size Not yet checked against the source | From your product UK standard block face. |
| Joint | 10 mm | Common UK size Not yet checked against the source | From your product Standard UK mortar joint. |
| Waste allowance | 10 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Droppings and mixing loss. |
| Mix ratio: parts sand to 1 part cement | 5 parts sand to 1 cement | Our assumption Not yet checked against the source | Our choice: change it to suit your job Check your maker's or builder's spec; the right ratio depends on the job. |
| Dry-volume factor | 1.3 × | Our assumption Not yet checked against the source | Our choice: change it to suit your job Dry materials shrink when mixed with water. Researcher to check against cement makers' guidance. |
| Cement density | 1440 kg/m3 | Our assumption Not yet checked against the source | Our choice: change it to suit your job Typical planning figure with no source yet. Researcher to source it and reclassify as typical. |
| Building sand density | 1.5 t/m3 Sources range 1.4–1.6 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) |
| Cement bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common UK cement bag. |
| Yield per pre-mixed bag | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product Enter the yield printed on your pre-mixed mortar bag. |
FAQs
Guides
Mortar mix ratios explained
What a mortar ratio like 1:4 or 1:5 means, where the right ratio is specified, wet vs dry volume, and when pre-mixed bags make sense.