Mortar Calculator
Calculate cement bags and sand volume for brick or block mortar, render coats and masonry bedding, based on area, joint thickness and mix ratio.
What this calculates
Calculates the mortar volume, cement bags and sand needed for a masonry or render application based on area, layer thickness and mix ratio.
Formula used
Volume = length × height × thickness. Volume with waste = volume × (1 + waste %). Cement bags = volume × bags/m³ (by ratio). Sand = volume × 1.05 m³/m³.
Worked example
A wall of 4 m × 2.5 m with 1.5 cm joints and 1:4 mix: volume = 0.15 m³. With 10% waste: 0.165 m³. Cement: ceil(0.165 × 11) = 2 bags. Sand: 0.165 × 1.05 ≈ 0.17 m³.
Mix ratio guide
1:3 (strong): exposed masonry, below-grade or high-humidity walls. 1:4 (standard): most exterior and interior brick or block walls. 1:5 (lean): lightweight interior partitions, basecoat render, non-structural applications.
When not to use this calculator
Pre-blended mortar products (dry-bag mixes) have their own coverage rates — use the manufacturer's data instead. This calculator is for site-batched mortar.
Frequently asked questions
What cement-to-sand ratio should I use?
1:3 for structural/exposed masonry. 1:4 for standard walls. 1:5 for lightweight interior or render coats.
How many bags per m²?
With 1:4 mix and 1.5 cm thickness: about 0.5 bags (25 kg) per m². Thicker joints need more.
What's the difference between mortar and concrete?
Mortar has no coarse aggregate (gravel). It bonds bricks and blocks. Concrete adds gravel for structural strength.
How thick should mortar joints be?
Brick: 10–15 mm. Concrete block: 10–20 mm. Render coat: 10–15 mm per coat.
Assumptions
- 1:3 mix: 14 bags (25 kg) per m³. 1:4: 11 bags. 1:5: 9 bags.
- Sand: 1.05 m³ per m³ of mortar in all cases.
- Does not include water, admixtures or tools.
- Waste applied to net mortar volume.
Actual cement consumption varies with cement type, sand grading and water content. Always conduct trial mixes for structural applications.
Common mistakes
- Adding too much water — this reduces mortar strength.
- Using dirty or clay-rich sand.
- Not dampening dry bricks before laying — they absorb water from the mortar.