How Much Mortar Do I Need? Bags and Cubic Feet for Brick and Block

Modular brick with 3/8 in joints takes about 5.5 cubic feet of mortar per 100 sq ft of wall, plus 15 to 25% waste (BIA). By the bag, one 80 lb mix lays up to 37 bricks or 13 blocks (QUIKRETE label).

A 20 × 8 ft wall with a door (139 sq ft net) needs about 9.2 cubic feet of mortar in modular brick, or 27 bags of 80 lb mix. In 8×8×16 block, the same wall takes 10 bags by the NCMA rate or 13 by the QUIKRETE label.

How do you calculate how much mortar a wall needs?

by volume (brick, BIA):
   mortar (cu ft) = net wall area ÷ 100 × 5.5 × (1 + mortar waste)
by the bag (brick or block):
   bags = ceil( units ÷ units per 80 lb bag )
net wall area = length × height − openings

1. Find the net wall area in square feet: length × height, minus doors and windows. The square footage calculator handles gables and steps.
2. Get the unit count from the guide for your unit: bricks per square foot or how many concrete blocks.
3. For brick mortar by volume, multiply the area by 5.5 cubic feet per 100 sq ft, then add 15 to 25% for waste.
4. For bagged mix, divide the units by the units one bag lays, using the label of the mortar you will buy, and round up.

The 5.5 cubic feet is the Brick Industry Association (BIA) figure for modular brick with 3/8 in joints, which is 8.1 cubic feet per 1,000 bricks. Standard-size brick uses 14.5 cubic feet per 1,000. Block mortar is quoted by the bag rather than by the cubic foot in the sources used here.

How much mortar does a brick wall need?

Modular brick, 3/8 in joints, running or stack bond, 5% brick waste and 20% mortar waste. Bags use the QUIKRETE rate of 37 bricks per bag on the bricks to buy.

The two mortar columns are by volume (BIA) and the bag column is by the product label (QUIKRETE). They come from different sources, and this guide does not convert one into the other: the bag yield in cubic feet is not on the data sheet. To convert cubic feet to cubic yards, divide by 27: 6.6 cubic feet is 0.24 cubic yards.

How many bags of mortar per 100, 500 and 1,000 bricks or blocks?

Divide the unit count by the units one bag lays and round up. Use the number of units you will lay. A label that says “up to” is a ceiling, so round up.

NCMA’s table also gives 50 brick-size concrete units (2-2/3 × 8 in face) per preblended 80 lb bag, so 1,000 of those take 20 bags. The NCMA rate assumes face-shell bedding, where mortar goes on the outer shells of the block only, and its table includes a nominal allowance for waste. Per 100 sq ft of 8×16 block wall (112.5 blocks), the NCMA and QUIKRETE rates give 7.03 and 8.65 bags, so 8 or 9.

Worked example: a 20 × 8 ft wall with a door

• Gross area: 20 × 8 = 160 sq ft. Door: 3 × 7 = 21 sq ft. Net area: 160 − 21 = 139 sq ft.
• Brick. Bricks before waste: 139 × 6.75 = 938.25, and with 5% waste 986.
• Mortar by volume: 139 ÷ 100 × 5.5 = 7.645 cubic feet. With 20% waste: 7.645 × 1.20 = 9.17 cubic feet, or 0.34 cubic yards.
• Mortar by the bag: 938.25 ÷ 37 = 25.36, so 26 bags on the net count, and 986 ÷ 37 = 26.65, so 27 bags on the bricks you buy. Take 27 when the label says “up to”.
• Block (8×8×16). Blocks: 139 × 1.125 = 156.375 before waste, 165 with 5%.
• Mortar by the NCMA rate of 16 per bag: 156.375 ÷ 16 = 9.77, so 10 bags. By the QUIKRETE label of 13 per bag: 156.375 ÷ 13 = 12.03, so 13 bags.

The brick and block bag counts differ because they are different units laid at different rates, and each source states its own. Use the figure on the bag you buy.

How much waste should you add to mortar?

BIA says to add 15 to 25% to the net mortar quantity for waste, and this guide uses 20% as the middle of that range. Waste covers mortar that never ends up in a joint. The 15 to 25% applies to the BIA cubic-foot figure. NCMA’s per-bag table already includes a nominal waste allowance, and a “lays up to” label is already a ceiling, so do not stack another 25% on top of a bag count. BIA also notes that 1 cubic foot of loose, damp sand makes about 1 cubic foot of mortar, which matters only if you mix from separate ingredients.

Which rate should you trust: NCMA, BIA or the bag label?

For bagged mix, the label on the product you buy. QUIKRETE Mortar Mix No. 1102 says each 80 lb bag “will lay up to 37 standard bricks or 13 standard (8 in by 8 in by 16 in) blocks”, and its standard formulation is Type N mortar under ASTM C270 and C1714. NCMA’s 16 blocks per bag is a generic rate for preblended mortar, so it is higher than the label’s 13 and gives fewer bags. A mason’s rule of thumb quoted by BIA, eight bags of masonry cement per 1,000 modular bricks, is a rough figure for a different product that includes waste. The mortar type your wall needs, and the mix proportions for site-mixed mortar, come from the design and ASTM C270. Ask your mason or supplier.

What about tile mortar and thinset?

Tile mortar is a different product with a different calculation. Thinset is bought by coverage per bag at a given trowel size, not by units laid. The tile guide covers thinset and grout, and the tile calculator counts them. The figures in this guide are for brick and block.

Assumptions, common errors and limits

• Brick figures are for modular brick with 3/8 in joints. Standard, queen, king and utility brick, wide joints, and bond patterns with headers change the volume. Corners, returns, arches and gable ends add mortar.
• Stacking waste twice. A bag count taken from a table that already includes waste does not need another allowance.
• Using one product’s rate for another. 37 bricks per bag is QUIKRETE’s number for its mix, and another brand may differ.
• Mixing the unit. 5.5 is cubic feet per 100 sq ft. It is not bags.
• Counting gross area. Subtract door and window openings first.
• Mortar type and strength, ties, flashing, lintels, reinforcement, wall height and lateral support are design items. Ask your building department or a licensed engineer. This guide estimates quantities only.
• Mortar is cement-based and can irritate skin and eyes. QUIKRETE’s data sheet says to wear impervious gloves such as nitrile. Wear eye protection too.

Common questions