Mortar and grout are the two cement-based mixes that hold a masonry job together — but they're not interchangeable, and the bag math is different for each. Here's the practical version, with the numbers actual masons use at the supply house.
Mortar vs grout — what's the difference
Mortar is the bedding material between bricks, blocks, or stone. It's mixed thick enough to hold a shape on the trowel and supports the structural load above. Type N is the all-purpose mix above grade (750 psi). Type S is for load-bearing or below-grade work (1,800 psi). Type M is the heaviest, used for foundations and chimneys (2,500 psi).
Grout is the thinner mix that fills tile joints or pumps into hollow CMU cells around rebar. Tile grout in particular is what most homeowners are buying when they say "grout" — sanded for joints 1/8 in and wider, unsanded for tighter joints on polished or scratch-prone tile.
Brick mortar — the 7-bag rule
The standard estimate is 7 bags of 80-lb mortar per 1,000 modular brick at a 3/8 in joint. That maps to roughly 30 brick per bag once you account for tooling loss and partial bags at the end of the day. The rule moves with joint thickness:
- 1/4 in joint → ~9 bags per 1,000 brick
- 3/8 in joint → 7 bags per 1,000 brick (standard)
- 1/2 in joint → ~5 bags per 1,000 brick
Counterintuitive at first — wider joints use less mortar per brick because each brick takes up more wall area, so you lay fewer bricks per square foot. A 1/2 in joint reduces brick count from 6.86/ft² to about 6.4/ft².
Run the count on the mortar and grout calculator — it pairs with the brick calculator so you get bricks and mortar in one trip to the yard.
Tile grout — joint volume drives the bag count
Grout coverage is more sensitive to joint size than most people realize. The volume of grout per square foot of tile is:
grout per ft² = (tile_w + tile_l) ÷ (tile_w × tile_l) × 144 × joint_w × joint_d
Larger tiles use less grout per area because the joint length per square foot drops. A 12×12 floor at a 1/8 in joint (1/4 in deep) needs about 0.75 in³ of grout per ft². The same wall in 4×4 mosaic at a 1/4 in joint burns 4.5 in³/ft² — six times the grout for the same square footage.
Sanded vs unsanded
Sanded grout is the default for floor and most field tile. It uses fine silica sand to bulk up the mix, resist shrinkage cracks at wider joints, and survive foot traffic. Joints from 1/8 in up to 1/2 in.
Unsanded grout is what you use on tight rectified-edge porcelain (1/16 in joints), polished marble, and glass. The sand particles in regular grout would scratch the tile face. Coverage is the same calculation, different bag.
Epoxy grout is its own category — sealed, stain-proof, used in commercial kitchens and shower pans. Coverage drops by half because epoxy is denser, and the mix is mixed in 1-quart kits, not 25-lb bags.
Common mistakes
Buying the wrong grout for the joint width. Putting unsanded grout in a 1/4 in joint cracks and shrinks within weeks because there's not enough body to bridge the gap. Putting sanded grout on polished marble scratches the surface during float work.
Underestimating mortar for tall walls. A story-pole brick wall over 8 ft tall has more head joints per square foot of face than a short wall, and waste goes up because mortar boards stand farther from the work. Bump waste to 15% on anything over a single story.
Forgetting the manufacturer's coverage chart. Bag yields vary by 20-30% across brands. Custom Building Products and Mapei publish coverage charts on every product page — cross-check the calculator's estimate against the chart for the SKU you're buying.
Quick FAQ
How many 80-lb bags of mortar per 1,000 bricks? About 7 at a 3/8 in joint — the calculator scales this to your wall area.
Sanded or unsanded for shower walls? Sanded for any joint 1/8 in or wider. Unsanded for rectified subway tile with hairline joints.
How long does mixed mortar stay workable? 90 minutes max in cool weather, 60 in heat. Re-tempering with water past that point weakens the bond enough to fail code in some jurisdictions.
Estimate only. The mortar and grout calculator uses standard industry yields. Real coverage varies by product, mix design, joint tooling style, and substrate absorption. Verify with the manufacturer's published coverage chart for the specific bag SKU before ordering.