Mortar Calculator
Mortar is calculated from the joint volume, not from the wall volume. Choose brickwork, blockwork, render or screed, enter the size of the job, and this calculator returns the mortar volume plus the cement and building sand you need for your chosen mix.
Your measurements
Check your order
Your masonry order
- Check dimensions, openings and the material specification against the project plan.
- Confirm pack size or bag yield with the supplier and add the selected allowance only once.
- Plan delivery access, handling and the tools required by the chosen installation method.
Tools for this job
For brick and block work, a masonry trowel helps place the mortar into the bed and joints used in your estimate.
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- Place mortar in beds and joints
Brick trowel
MARSHALLTOWN Philadelphia brick trowel
For placing and spreading mortar when laying bricks or blocks. Choose a blade size you can handle comfortably and keep the specified bed and joint thickness consistent.
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How mortar quantity is worked out
For brickwork and blockwork the mortar volume is the wall volume minus the volume of the units themselves. A square metre of single-skin brickwork is 0.1025 m³ of wall containing about 0.085 m³ of brick, which leaves roughly 0.0176 m³ of mortar: about 17.6 litres per square metre before waste.
Blockwork uses far less. The same square metre in 440 x 215 x 100 mm blocks has only about 6.5 litres of joint, because there are ten joints instead of sixty.
Render and screed are simpler: area multiplied by thickness gives the volume directly.
The formulas
Worked example
A garden wall 5 m long and 2 m high in single-skin brickwork, 1:4 mix, 20% waste.
Area = 10 m². Bricks at 59.3 per m² = 593 bricks, or 623 with 5% for breakage. Mortar = 10 × 0.0176 = 0.176 m³, plus 20% = 0.21 m³.
Dry volume = 0.21 × 1.30 = 0.274 m³. Cement = 0.274 ÷ 5 = 0.055 m³ × 1440 = 79 kg, so four 25 kg bags. Sand = 0.219 m³ × 1600 = 350 kg, so one bulk bag with plenty to spare.
Which mix for which job
The old rule still holds: the mortar should always be weaker than the units it bonds. If the mortar is stronger, movement cracks the brick instead of the joint, and a cracked brick cannot be repointed.
| Mix | Where it is used | Notes |
|---|---|---|
| 1 : 3 | Below DPC, engineering brick, copings | Strong and dense, but brittle: not for soft bricks |
| 1 : 4 | General purpose, blockwork, first render coat | The default for most domestic work |
| 1 : 5 | External brickwork above DPC | Good balance of strength and flexibility |
| 1 : 6 | Internal blockwork, soft or reclaimed brick | Weaker than the brick, so cracks go in the joint |
| 1 : 1 : 6 (cement:lime:sand) | Period property, lime-compatible | Breathable and self-healing, slower to gain strength |
Bricks and blocks per square metre
| Unit | Size | Per m² | Mortar per m² |
|---|---|---|---|
| Standard brick, stretcher bond | 215 x 102.5 x 65 mm | 59.3 | 17.6 L |
| Standard brick, both skins of a cavity wall | as above x 2 | 118.6 | 35.2 L |
| Concrete block | 440 x 215 x 100 mm | 9.9 | 6.5 L |
| Concrete block, thin joint | 440 x 215 x 100 mm | 9.9 | 1.5 L |
| US modular brick | 194 x 92 x 57 mm | 74.6 | 19.2 L |
Why 20% waste is realistic
- Mortar dropped from the trowel and off the board. This alone is 5 to 10% for most people.
- What sets in the mixer, the bucket and the barrow before you get to it.
- Joints that end up 12 mm instead of 10 mm: a 20% overrun on its own.
- Perpend joints filled more generously than the theoretical minimum.
- Pointing and making good at the end of the job.
Sources and assumptions
Brick and block modes use estimated joint volumes for the stated standard units. Render and screed modes use area times thickness. Bag yield and the conversion from wet mortar to separate dry materials are approximations.
- QUIKRETE Mortar Mix 1102: technical data sheet: This sheet states the mortar type, product-specific mixing instructions and the approximate number of standard bricks or blocks laid per bag.
Before using this estimate
- The fixed joint-volume figures assume standard UK single-leaf brick or 100 mm blockwork. Frogs, hollow units, thick blocks and joint profiles can change consumption.
- A cement-to-sand ratio alone does not specify a compliant structural mortar, a lime mortar or a screed system. Confirm the chosen mix and actual bag yield with the supplier.
Source notes reviewed . See how we check calculations and handle corrections.
Planning your order
Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.
Published by OrderEnough. This is a planning estimate: check the product specification and the assumptions above before ordering. Last updated . Read how we source our figures on the methodology page.