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Mortar Calculator — How Much Cement and Sand Do I Need?
Calculate the cement and sand needed for mortar. Covers bricklaying, blockwork, pointing, and rendering with standard UK mix ratios.
Total wall area to be covered
Adds 10% extra for spillage and over-mixing
10% is standard for mortar work
Material Prices (optional)
Wet mortar density (default 1800 kg/m³)
Mortar weight per brick (default 0.9 kg ≈ 0.5 m³/1000)
Mortar weight per 100mm block (default 2.16 kg ≈ 0.012 m³/m²)
Safety notice
Structural elements must be designed or checked by a structural engineer before construction. Treat these figures as initial guidance for planning and budgeting, not a structural design.
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How We Calculate This
This calculator determines the volume of mortar needed, then breaks it down into cement and sand quantities based on your chosen mix ratio.
Mortar rates by application
- Bricklaying (half-brick stretcher): 0.03 m³ mortar per m² (≈ 0.5 m³ per 1000 bricks at 60 bricks/m², 10mm joints)
- Bricklaying (full-brick English/Flemish): 0.06 m³ mortar per m²
- Blockwork (100mm blocks, 10mm joints): 0.012 m³ mortar per m² (10 blocks/m², typical UK domestic; 215mm thick blocks need ~0.018)
- Pointing/repointing: 0.01 m³ mortar per m² (joints only, ~15mm rake-out depth)
- Rendering (15mm coat): 0.015 m³ mortar per m²
These are standard UK quantity-surveying rates (10mm joints), not figures from a single British Standard. Rates assume standard UK brick dimensions and bricks per m² — see our brick dimensions reference. For joint-only work, see our repointing calculator, which works out how much mortar to remove and replace when repointing from your joint width and raking depth.
Mix ratio material quantities
Per cubic metre of WET mortar (conservative yield rule of thumb — mortar volume ≈ sand volume):
- 1:3 (strong): ~19 bags cement (25kg), ~1.5 tonnes building sand
- 1:4 (general): ~14 bags cement (25kg), ~1.5 tonnes building sand
- 1:5 (internal): ~12 bags cement (25kg), ~1.5 tonnes building sand
- 1:6 (internal sheltered): ~10 bags cement (25kg), ~1.5 tonnes building sand
Cement bags derived from loose cement bulk density 1,440 kg/m³ ÷ 25 kg/bag and the yield assumption that mortar volume ≈ sand volume (the cement paste fills the voids between sand grains). Sand mass uses building sand bulk density ~1,500 kg/m³ (graded per BS EN 13139). These are deliberately generous quantity-surveying estimates so a job does not run short — they are not values published in a British Standard, and an alternative combined dry-volume method gives roughly 25-30% fewer cement bags.
Standards & mortar designations
Masonry mortar should comply with BS EN 998-2 (Specification for mortar for masonry — masonry mortar; note BS EN 998-1 is the separate standard for rendering/plastering mortar). The designation is selected from exposure conditions per PD 6697 / BS 5628-3:
- (i) M12 — cement:sand 1:3: chimneys, parapets and walls below DPC.
- (ii) M6 — cement:sand 1:3 to 1:4: general external walls.
- (iii) M4 — cement:lime:sand 1:1:5-6, or cement:sand 1:5-6 with plasticiser: most sheltered domestic work. A plain 1:5-6 cement:sand mix with no lime or plasticiser is weaker than M4.
- (iv) M2 — cement:sand 1:7-8: internal, sheltered, low-stress only.
Designation proportions per PD 6697 / BS 5628-3 (also reflected in BS EN 1996-1-1 UK guidance). Adding lime or a liquid plasticiser improves workability and is what lets a 1:5-6 cement:sand mix reach the M4 class.
Working figures for this are collected in our Mortar Mix Ratios reference table.
Working figures for this are collected in our Mortar Suction Rates reference table.
Frequently Asked Questions
A 1:4 mix (one part cement to four parts building sand) is the standard general-purpose mortar for most bricklaying. Use a stronger 1:3 mix for exposed walls, below DPC, and chimney stacks. A weaker 1:5 mix is acceptable for internal walls in sheltered conditions. Adding plasticiser improves workability. If you're rendering a wall rather than laying bricks, use our sand and cement render mix ratio calculator instead — render uses sharp sand at 1:5 (1:4 for the scratch coat), not building sand.
For stretcher bond (half-brick wall) with 10mm joints, you need approximately 0.5 m³ of mortar per 1000 bricks (the standard quantity-surveying rate at 60 bricks/m² × 0.03 m³/m²). At a 1:4 cement:sand mix that works out to around 7 bags of 25kg cement (8 bags with 10% wastage) plus about 0.75 tonnes of building sand. Always add 10-15% extra for wastage. Use our Brick Calculator to work out how many bricks you need, or our Block Calculator for concrete blocks.
Use building sand (also called soft sand or bricklaying sand) for mortar, not sharp sand. Building sand is finer and smoother, which makes the mortar workable and easier to lay. It should comply with BS EN 13139. The sand colour will affect the final mortar colour.
That's correct and intentional. This calculator uses the common 'yield' rule of thumb where 1 m³ of finished mortar is taken to need roughly its own volume of sand (about 1.5 tonnes at 1500 kg/m³), because the cement paste largely fills the voids between the sand grains rather than adding much extra bulk. On that basis the sand quantity for a given mortar volume is independent of the ratio — what changes is the cement: stronger 1:3 needs ~19 bags/m³, standard 1:4 ~14, sheltered 1:5 ~12, and 1:6 ~10 (25kg bags). These are deliberately generous trade estimates so you don't run short; an alternative 'combined dry-volume' method gives roughly 25-30% fewer cement bags. They are quantity-surveying figures, not values published in a British Standard — the mortar's specification and strength class are governed by BS EN 998-2 (masonry mortar), with mix designations from PD 6697 / BS 5628-3.
Yes, liquid plasticiser (such as Feb-Mix) is the modern alternative to lime in mortar. It improves workability, making the mix 'fatty' and easier to work with. Use it according to the manufacturer's instructions — typically one capful per mix. It also helps frost resistance in cold weather.
Mortar takes approximately 24-48 hours for an initial set and 28 days for full cure. Do not lay bricks or blocks if the temperature is below 2 degrees Celsius or dropping, as frost can destroy fresh mortar. In hot weather, dampen bricks before laying to prevent them drawing moisture from the mortar too quickly.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.