Mortar Calculator UK: Sand and Cement for Bricks and Blocks
Enter a wall size, a wall area, a brick count or a repointing job. This mortar calculator then works out the cement, building sand, lime and plasticiser. It also shows the ready-mixed bags you would need instead.
More free UK building calculators
Mortar is only one component of the project. These calculators cover the bricks, blocks and footings surrounding it.
Bricks per m², mortar and cost for any wall.
Concrete, breeze and aircrete blocks, with mortar and cost.
Cubic metres, bags, cement and ballast for slabs and footings.
MOT Type 1, ballast, sand and gravel in tonnes and bulk bags.
Tiles per m², boxes and wastage for floors and walls.
Adhesive per m² and 20 kg bags by trowel notch.
Grout per m² from tile size, joint width and depth.
Litres and tins for rooms, walls, ceilings and exteriors.
Rise, going, pitch and stringer length, with Part K checks.
Tonnage, coverage and driveway cost per m².
Why mortar estimates go wrong
Picture this. The fourth course is going down nicely when the mixer scrapes empty. Every cement bag is empty, and the builders’ merchant closed at lunchtime.
Mortar left on the board stiffens within a couple of hours. Tomorrow’s fresh batch may also dry to a slightly different shade. That colour band can stay visible in your wall for decades.
Over-order instead, and opened cement bags gradually harden in the shed. So how do you purchase the correct quantity immediately?
Our rule: measure the wall, pick the mix your bricks need, then add 5% for droppings. Buy every bag of cement and sand for one wall together.
How much mortar per m² of brickwork?
A half-brick wall holds approximately 0.018 m³ of wet mortar per m². At 1:4, that takes 7.7 kg of cement and 34 kg of building sand, before wastage.
How much mortar for 1,000 bricks?
One thousand standard bricks need approximately 0.3 m³ of mortar. That equals six 25 kg bags of cement and one bulk bag of building sand. Each brick takes roughly 0.3 litres.
How to use the mortar calculator
Select the tab that matches the information you already have. Think of it as a complete mortar estimator for brick and block walls.
- Choose how to measure. Use Wall size, Wall area, Brick count or Repointing.
- Pick bricks, blocks or a custom unit. Standard UK sizes are preset, including aircrete jumbo blocks.
- Enter the wall. Use metres or feet, set single or double skin, and deduct doors and windows.
- Choose the mortar mix. Options range from strong 1:3 to traditional cement, lime and sand mixes.
- Check the joint and wastage. Keep 10 mm joints and 5% wastage unless your specification differs.
- Add prices if you like. The tool then compares mixing on site with buying ready-mixed bags.
The result lists cement bags, sand in kilograms or bulk bags, lime, plasticiser and the mortar volume. Still counting bricks? Our brick calculator gives the wall’s brick total first.
How much mortar do I need? The formula
Mortar fills the bed joints and perpends surrounding every individual brick. Therefore, calculate the joint area on the wall face, then multiply it by the wall thickness.
Why 1.52? Dry materials shrink considerably when you add water, because cement particles fill the spaces between sand grains. Our brick and block calculators use exactly the same factor, so every estimate stays consistent.
Sand and cement per m² for every mortar mix
| Mix | Per m² of brickwork | Per 1,000 bricks |
|---|---|---|
| 1:3 strong | 9.6 kg cement, 32 kg sand | 163 kg cement, 542 kg sand |
| 1:4 general purpose | 7.7 kg cement, 34 kg sand | 130 kg cement, 578 kg sand |
| 1:5 moderate | 6.4 kg cement, 36 kg sand | 108 kg cement, 602 kg sand |
| 1:6 lean | 5.5 kg cement, 37 kg sand | 93 kg cement, 620 kg sand |
| 1:1:6 cement, lime, sand | 4.8 kg cement, 1.7 kg lime, 32 kg sand | 81 kg cement, 28 kg lime, 542 kg sand |
| 1:2½ NHL 3.5 lime | 5 kg lime, 31 kg sand | 84 kg lime, 516 kg sand |
Standard 215 × 102.5 × 65 mm bricks, 10 mm joints, single skin, before wastage. Calculated with the tool on this page.
Mortar calculator examples for real UK projects
We ran each project through the calculator, including 5% mortar wastage unless otherwise noted.
Case study 1: garden wall
A 6 m long, 1.8 m high single skin wall in standard bricks, laid in 1:4 mortar
The bulk bag leaves roughly 460 kg of sand spare. Cover it properly, and it remains usable for the coping or another project.
Case study 2: blockwork for an extension
A 14 × 2.4 m inner leaf in 100 mm blocks, less 4.4 m² of openings
Case study 3: frogged bricks laid frog up
1,000 frogged bricks at 1:4, with the frogs filled
Bricklayers lay frogs upward for strength in loadbearing work. Always confirm the bricklaying orientation before ordering.
Case study 4: repointing a Victorian terrace
30 m² of soft red brick, raked out 20 mm, with 15% wastage
Older bricks need the softer, more breathable lime mix. Hard cement pointing traps moisture and pushes frost damage into the brick face.
Which mortar mix ratio should you use?
UK guidance organises mortar into designations and compressive strength classes. A stronger mix is not automatically better. Mortar should remain weaker than the bricks, so any cracking follows the joints instead.
| Class | Cement : lime : sand | Cement : sand with plasticiser | Typical use |
|---|---|---|---|
| M12 | 1 : 0–¼ : 3 | 1:3 | Copings, retaining walls and work below ground |
| M6 | 1 : ½ : 4–4½ | 1:3–4 | Exposed walls, garden walls and work below the DPC |
| M4 | 1 : 1 : 5–6 | 1:5–6 | Most house walls above the DPC |
| M2 | 1 : 2 : 8–9 | 1:7–8 | Internal walls and sheltered work |
Proportions by volume. Based on the Hanson hydrated lime data sheet and PD 6678. Your designer or brick maker has the final say.
Most DIY garden walls use 1:4 with plasticiser, often called a 4:1 mix. Bricklayers usually mention the sand first, so 4:1 and 1:4 describe identical mortar. Likewise, a 5:1 mix suits sheltered masonry above the DPC. Engineering bricks and copings deserve the stronger 1:3.
Mortar calculator for blockwork
Blocks need considerably less mortar per m² than bricks, because their larger faces create fewer joints. Block thickness matters more than face dimensions. To estimate mortar for a block wall, choose Blocks on the Wall size tab.
| Block | Per m² of wall | Per 100 blocks |
|---|---|---|
| 440 × 215 mm, 100 mm thick | 2.9 kg cement, 13 kg sand | 29 kg cement, 129 kg sand |
| 440 × 215 mm, 140 mm thick | 4 kg cement, 18 kg sand | 41 kg cement, 181 kg sand |
| 440 × 215 mm, 215 mm thick | 6.2 kg cement, 28 kg sand | 63 kg cement, 278 kg sand |
| 630 × 215 mm aircrete, 100 mm | 2.6 kg cement, 12 kg sand | 37 kg cement, 166 kg sand |
1:4 mix, 10 mm joints, single skin, before wastage. Calculated with the tool on this page.
Need the block count first? Our block calculator handles concrete, breeze and aircrete blocks. Thin-joint aircrete systems use a 3 mm proprietary mortar, so follow the maker’s bag coverage instead.
Repointing mortar calculator: mortar per m² by depth
Repointing replaces only the outer section of each joint. The rake-out depth therefore determines the quantity.
| Rake-out depth | Per m² at 1:4 | One 25 kg bag of cement covers |
|---|---|---|
| 10 mm | 0.8 kg cement, 3.3 kg sand | about 33 m² |
| 15 mm | 1.1 kg cement, 5 kg sand | about 22 m² |
| 20 mm | 1.5 kg cement, 6.7 kg sand | about 17 m² |
| 25 mm | 1.9 kg cement, 8.4 kg sand | about 13 m² |
Standard bricks with 10 mm joints, about 17 m of joint per m², before wastage. Allow 15% for repointing droppings.
Historic England advises matching the original mortar and raking out by hand. Its free guide, Repointing Brick and Stone Walls, explains joint profiles and lime mixes. Flaking brick faces near hard pointing? Read our guide to spalling bricks before you start.
Lime, plasticiser or ready-mixed mortar?
Three decisions affect your shopping list more than the wall size.
- Plasticiser: it introduces tiny air bubbles, so a lean mix remains workable and resists frost. Typical liquid products need about 125 ml per 25 kg bag of cement.
- Hydrated lime: it replaces plasticiser in cement, lime and sand mixes such as 1:1:6. Lime improves water retention and lets mortar heal hairline cracks.
- NHL lime: natural hydraulic lime suits pre-1919 buildings with soft bricks. It requires no additional cement.
- Ready-mixed bags: you simply add water. Each 25 kg bag lays approximately 35 bricks, so they suit small repairs and isolated patches.
In our opinion, plasticiser belongs in nearly every cement mix. It prevents anyone adding unnecessary cement simply to make spreading easier. For anything over a few square metres, site mixing costs roughly half as much as ready-mixed bags.
How much does mortar cost in 2026?
We checked UK merchant and DIY store listings in October 2026. Prices vary considerably by region, brand and delivery charge.
| Material | Typical price (2026) | Notes |
|---|---|---|
| Cement, 25 kg | about £7.50–£8.50 | General purpose Portland cement |
| Building sand, bulk bag | about £47–£77 | Roughly 800–850 kg, plus delivery |
| Hydrated lime, 25 kg | about £14–£28 | Merchants vary widely |
| Ready-mixed mortar, 25 kg | about £8.70–£10.60 | Add water only |
| Mortar plasticiser, 5 L | about £7.60–£9 | Treats around 40 bags of cement |
Prices include VAT where shown. Check your local branch before ordering.
For the garden wall in case study 1, site-mixed materials cost about £97. Twenty ready-mixed bags would cost around £180. That works out at roughly £5 of mortar materials per m² of brickwork. Pricing a whole build? Our brick calculator adds bricks, mortar and cost together, and the aggregate calculator converts sand in bulk bags.
Common mortar mistakes we see
Developing this calculator changed our perspective. We expected most people to underestimate the cement. In reality, many underestimate the sand, because a bulk bag weighs less than they imagine.
- Measuring by the shovel. Use a bucket or gauge box, so every batch stays consistent.
- Making mortar too strong. Extra cement causes shrinkage cracks and can damage soft bricks.
- Retempering old mortar. Discard any batch that has started to stiffen.
- Laying in frost. Stop work below about 3°C, and cover new brickwork overnight.
- Leaving sand uncovered. Wet sand weighs more and alters your mix proportions.
Wet cement burns skin, so wear waterproof gloves and eye protection. The HSE guidance on cement explains how to work safely. Our step-by-step brick wall guide covers mixing and laying in detail.
Mortar calculator FAQs
How our mortar calculator works out the figures
The calculator uses the UK coordinating size of each brick or block, which adds a 10 mm joint. It multiplies the joint area by the wall thickness to find the wet mortar. Dry material equals 1.52 times that volume, plus your wastage.
We convert cement at 1,440 kg/m³ and dry building sand at 1,600 kg/m³. Hydrated lime uses 500 kg/m³, which turns each volume into a weight. These figures match our brick and block calculators exactly. Every case study on this page came straight from the tool.
Remember that empty mixer on the fourth course? Ten minutes with a tape measure would have prevented it. Last reviewed: October 2026. Treat results as estimates, and follow the mortar your designer specifies.
What are you building next, and which mix will you use? Tell us through our contact page. Your questions help us improve the calculator.