Mortar Calculator
Work out how many bags of mortar you need - enter your wall size and whether you are laying block or brick to get the unit count and the 80 lb mortar bags, based on manufacturer yields.
United States — national average · 2026 prices
Material only unless stated as installed. Excludes tax, permits and local labour. Verify with local suppliers — see how we calculate.
How this calculator works
Every figure above comes from the formula below, applied to the assumptions listed. Nothing is looked up from a hidden table — you can reproduce the result by hand.
Formula
wall area = length × height
units = area × units per sq ft (8×8×16 block = 1.125 · modular brick = 6.75)
bags = units × (1 + waste ÷ 100) ÷ per-bag yield, rounded up
per-bag yield (80 lb): 13 blocks or 37 bricks
Assumptions & limits
- Per-bag yields are the QUIKRETE Mortar Mix data-sheet figures: one 80 lb bag lays up to 37 standard bricks or 13 standard 8×8×16 blocks. Other brands land close; check the printed yield on your bag.
- Units per square foot assume standard 3/8 inch joints: 1.125 blocks or about 6.75 modular bricks per sq ft of wall face.
- Default waste is 10% — dropped mortar, re-buttering and full joints. First-time layers should round up.
- Bag price defaults to $9 for an 80 lb bag of mortar mix.
- Mortar TYPE (N for general above-grade, S for structural and below-grade, M for heavy loads) is a specification question this calculator does not decide — match it to the application and the unit manufacturer’s guidance.
- Counts cover the mortar. Block fill, grout, rebar dowels and wall reinforcement are separate materials with their own rules.
Worked example
A 20 ft long, 6 ft high wall in 8×8×16 block, 10% waste, $9 per bag
- Wall area = 20 × 6 = 120 sq ft
- Blocks = 120 × 1.125 = 135
- With 10% waste = 148.5 → 148.5 ÷ 13 = 11.4 → 12 bags
- Cost = 12 × $9 = $108
Result:12 × 80 lb bags of mortar mix for a 135-block wall — roughly $97 to $124.
Built and maintained by Christoph Ballmer, Honeygoat GmbH
Method and constants last checked against the calculator code on August 25, 2026. Independent trade review is not yet in place for this calculator — see how we handle review.
Read the site-wide calculation methodology · estimate vs. quote and safety limits
How mortar is estimated
Mortar quantity follows the units you are laying, and the units follow the wall face. With standard 3/8 inch joints, a square foot of wall holds about 1.125 concrete blocks (8×8×16) or about 6.75 modular bricks. From the unit count, the per-bag yield does the rest — and that yield is a published manufacturer figure, not folklore: per the QUIKRETE Mortar Mix data sheet, one 80 lb bag lays up to 37 standard bricks or 13 standard blocks.
bags = wall area × units per sq ft × (1 + waste%) ÷ per-bag yield
The 10% waste default is honest, and first-timers should raise it: dropped mortar, boards that need re-buttering and joints run full all consume mix that never ends up in the wall.
Mortar types: N, S and M
| Type | Strength | Where it belongs |
|---|---|---|
| Type N | ≈ 750 psi | General above-grade walls, veneer, chimneys |
| Type S | ≈ 1,800 psi | Below grade, retaining walls, structural block |
| Type M | ≈ 2,500 psi | Heavy loads, engineered masonry |
Stronger is not automatically better — mortar should be slightly weaker than the units it binds, so hairline movement cracks the joint (repairable) rather than the block or brick. Match the type to the application and the unit manufacturer's guidance.
Bagged mix or site-mixed?
Bagged mortar mix needs only water, which is the entire point: the cement-to-sand proportioning is already done and consistent bag to bag. Site-mixing — one part masonry cement to 2.25–3 parts damp sand by volume — pays off on big jobs where dozens of bags would be mixed anyway. Either way, mix only what gets used in about 90 minutes; retempering old mortar with extra water costs bond strength.
The rest of the wall
This calculator counts mortar and units. A block wall also needs a concrete footing below frost depth — size it with the concrete calculator — and structural walls take grout and rebar dowels per the code. A garden wall in stacked segmental block needs no mortar at all: that is the retaining wall calculator's territory. Bagging concrete for the footing? The concrete bags calculator counts those.
Yields are the manufacturer's laboratory figures — real-world consumption runs higher, which the waste allowance covers. Check the printed yield on the brand you actually buy, and confirm structural requirements with your building department.
Frequently asked questions
How do you calculate how much mortar you need?
Work from the wall face: an 8x8x16 block wall has about 1.125 blocks per square foot, a modular brick wall about 6.75 bricks per square foot with standard 3/8 inch joints. Then divide the unit count by the per-bag yield - one 80 lb bag of mortar mix lays up to 13 standard blocks or 37 standard bricks per the QUIKRETE data sheet. The calculator above adds a 10% waste allowance on top.
How many bags of mortar do I need for 100 blocks?
At the data-sheet yield of 13 standard 8x8x16 blocks per 80 lb bag, 100 blocks take 100 / 13 = 7.7 - call it 8 bags, or 9 with the usual 10% waste allowance. First-time block layers drop and re-butter more mortar than they expect, so rounding up is the right instinct.
How many bricks will one bag of mortar lay?
Up to 37 standard bricks per 80 lb bag of mortar mix, per the manufacturer data sheet. Real-world figures land lower - 30-35 is common once joints run a little full and some mortar hits the ground - which is what the waste allowance is for.
Do you mix mortar by weight or volume?
Bagged mortar mix needs only water - the cement-to-sand proportioning is already done, which is the point of buying it bagged. Site-mixed mortar is batched by VOLUME: one part masonry cement to 2.25-3 parts damp loose sand, per the masonry standards. Mix only what you can use in about 90 minutes.
What type of mortar should I use?
Type N is the general-purpose choice for above-grade walls and standard veneer. Type S carries higher strength for below-grade work, retaining walls and anything structural. Type M is for heavy loads and is rarely a DIY pick. Match the type to the application and check what your block or brick manufacturer specifies - strength and bond are a pairing, not a maximum.