Mortar Calculator — Bags Needed for Brick or Block Walls
Mortar coverage depends on the type of work — bricklaying, blockwork, and pointing all use different amounts. This calculator uses your wall area and the coverage figure printed on your mortar bag to give you an accurate bag count.
How we calculate
Wall area = length × height. Area with waste = wall area × (1 + waste %). Bags = ⌈area with waste ÷ bag coverage⌉.
Worked example
4 m × 2 m wall = 8 m². With 10% waste: 8.8 m². At 2.5 m²/bag: ⌈8.8 ÷ 2.5⌉ = 4 bags.
Common mistakes
- Using the bricklaying coverage figure for pointing — repointing uses far less mortar per m².
- Mixing too much mortar at once — it goes off in 1–2 hours and cannot be re-tempered.
- Not using a plasticiser — it makes mortar workable and reduces the risk of cracking.
- Applying mortar in direct sun or high wind — it dries too fast and loses strength.
Frequently asked questions
How many bags of mortar do I need per square metre?+
For standard bricklaying, one 25 kg bag covers approximately 2–4 m² of wall face. Blockwork typically uses less mortar than bricklaying because blocks are larger and there are fewer joints. Always check your bag label for the stated coverage.
How long does mixed mortar last?+
Mixed mortar is workable for about 1–2 hours at normal temperatures. Mix only what you can use in that time — re-tempering (adding water to stiffened mortar) weakens it. In hot or windy conditions, mix smaller batches more frequently.
What mortar mix ratio should I use?+
A standard general-purpose mix is 1 part cement : 4–6 parts sand. Stronger mixes (1:3) are used below ground or in exposed locations. Weaker mixes (1:6) suit softer bricks that could crack under a strong mortar. Premixed bags include plasticiser and are pre-proportioned.
Can I use the same mortar for pointing and bricklaying?+
Not always. Pointing (repointing old joints) uses the same mix but is applied in smaller quantities. Some pointing products are specifically formulated for aesthetics and flexibility. For structural bricklaying, use a standard cement:sand mortar.