Mortar Calculator — How Much Cement and Sand Do I Need?

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.