To estimate mortar, divide the wall area by the area one bag of mortar lays for your unit, then add a waste allowance and round up to whole bags. Coverage depends on whether you are laying brick or block and the joint size, so it is read from the bag or a coverage chart. For 100 sq ft of brick at 15 sq ft per bag with 10% waste, you need 8 bags.
Mortar Calculator — bags for a brick or block wall
Mortar for 100 sq ft of wall at 15 sq ft per bag.
- Area covered (sq ft)
- 120
Quick examples
How it's calculated
- Bags = area × (1 + waste) ÷ coverage per bag, rounded up
- area
- = 100
- coverage
- = 15
- 8
How it works
Mortar is estimated by wall area, since a bag of mortar mix lays a certain area of masonry, per Wolfram MathWorld's A = length × width:
- Wall area — length × height of the wall in square feet.
- Coverage per bag — how much wall one bag lays. This depends on the unit (brick uses more mortar per square foot than block) and the joint thickness, so it comes from a coverage chart — roughly 12–18 ft² per bag for brick and 25–35 ft² for block are common.
- Bags = area ÷ coverage per bag, times (1 + waste %), rounded up to whole bags.
Because coverage varies so much between brick and block, the calculator takes it as an input. A waste allowance of about 10% covers spillage, dropped mortar and the extra needed for a rough or uneven wall. You will also need masonry sand to mix with the mortar cement — follow the bag's mixing ratio.
Worked example
For a 100 ft² brick wall at 15 ft² per bag, before waste you need 100 ÷ 15 ≈ 6.67 bags. Adding 10% waste gives 6.67 × 1.1 ≈ 7.33, rounded up to 8 bags, which lay 120 ft².
Frequently asked questions
How many bags of mortar do I need?
- Divide the wall area by the coverage one bag provides, add a waste allowance, and round up. For 100 sq ft of brick at 15 sq ft per bag with 10% waste, that is 100 ÷ 15 × 1.1 = 8 bags.
Why does coverage differ between brick and block?
- Brick is smaller and has more joints per square foot, so it uses more mortar; block is larger with fewer joints, so a bag goes further. Joint thickness also matters — thicker joints use more mortar.
How much mortar per 100 bricks?
- As a rough guide, about 2.5–3 bags of mortar mix lay 100 standard bricks, depending on brick size and joint width. Estimating by wall area, as this calculator does, is usually simpler.
Do I need sand as well?
- Yes, if you buy mortar cement rather than pre-mixed mortar. Mortar is cement mixed with masonry sand and water in a set ratio printed on the bag. Pre-mixed mortar already includes the sand.
How much waste should I add?
- About 10% is typical, covering spillage and dropped mortar. A rough or uneven wall, or a beginner mason, may waste more — add up to 15%.
How do I measure a wall with openings?
- Multiply length by height for the full wall, then subtract the area of large openings such as windows and doors before dividing by the coverage per bag.
How we know this is right
- Last reviewed
- Aug 8, 2026
- Precision
- Rounded to 0 decimal places.