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 (~1kg per brick — NHBC 6.1)
• Bricklaying (full-brick English/Flemish): 0.06 m³ mortar per m²
• Blockwork (100mm blocks, 10mm joints): 0.012 m³ mortar per 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

Mix ratio material quantities

Per cubic metre of WET mortar (yield assumption per BRE Digest 362, NHBC 6.1, BS EN 998-1):

• 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, M4): ~10 bags cement (25kg), ~1.5 tonnes building sand

Cement bags derived from cement bulk density 1,440 kg/m³ ÷ 25 kg/bag and the yield assumption that mortar volume ≈ sand volume (cement fills voids in sand for 1:3 to 1:6 ratios). Sand mass uses building sand bulk density 1,500 kg/m³ per BS EN 13139.

Standards

Mortar should comply with BS EN 998-2 (Specification for mortar for masonry). Mortar designation should be selected based on exposure conditions per BS 5628 / PD 6697. General-purpose mortar (M4 designation iii, ~1:5 to 1:6) is suitable for most sheltered domestic applications; M6 (~1:4) for general external walls; M12 (~1:3) for chimneys and walls below DPC.