How Much Mortar Do I Need?
Estimating mortar correctly helps prevent wasted material, unnecessary store trips and delays while a wall is being laid. Mortar requirements change with brick or block dimensions, joint thickness, wall layout, workmanship, bag yield and job-site waste. This guide explains a practical estimating method, common units and joints, a worked example and buying tips. The free Mortar Calculator performs the same calculations automatically in Imperial or Metric units and can include optional material cost.
What Is Mortar?
Mortar is a workable mixture used to bond masonry units together. It fills bed and head joints, accommodates small differences between units and helps distribute loads through a masonry assembly. Common applications include clay brick, concrete block and many stone-veneer systems.
Mortar is not the same as concrete. Mortar is formulated for bonding and joint work and normally uses finer aggregate. Concrete commonly contains coarse aggregate and is intended to form structural masses such as slabs, beams and footings. Use the product and mortar type specified for the masonry system rather than substituting concrete.
How Mortar Is Estimated
Start with gross wall area: wall length × wall height. Calculate each wall section separately when the project has different heights or materials.
Measure large doors, windows and other openings, then subtract their combined area. Net wall area = gross wall area − opening area. The Mortar Calculator treats the dimensions entered as net wall area, so divide a wall around openings into rectangular sections when needed.
Choose the actual masonry-unit size. Unit length and height plus the mortar joint determine how many bricks or blocks fit within the net wall area.
Nominal unit face = (unit length + joint thickness) × (unit height + joint thickness). Estimated units = net wall area ÷ nominal unit face.
Convert estimated units into mortar volume using a typical volume per 1,000 units for the selected brick or block. Adjust that rate for the selected joint thickness.
Divide mortar volume by the mixed yield printed on the bag to estimate bags. Add a practical waste allowance for board loss, dropped mortar, tooling, cleanup and variation, then round the purchase quantity up to whole bags.
Common Mortar Joint Size Reference
| System | Joint Size | Planning Note |
|---|---|---|
| Imperial | 3/8 in | Common baseline planning joint for brick and block |
| Imperial | 1/2 in | Thicker joint that generally increases mortar volume |
| Metric | 10 mm | Common baseline Metric planning joint |
| Metric | 12 mm | Thicker Metric option that generally uses more mortar |
Why Joint Thickness Matters
Thicker bed and head joints occupy more volume between masonry units, so they generally require more mortar. Joint depth and profile also matter: tooled, raked, struck and other profiles do not necessarily leave the same finished volume.
Use the joint specified by the plans, masonry-unit manufacturer or mason. Joint thickness should not be changed only to reduce the bag estimate.
Common Masonry Unit Reference
| System | Unit | Typical Actual Dimensions |
|---|---|---|
| Imperial | Modular brick | 7 5/8 in × 3 5/8 in × 2 1/4 in |
| Imperial | Queen brick | 9 5/8 in × 3 5/8 in × 2 3/4 in |
| Imperial | King brick | 9 5/8 in × 2 3/4 in × 2 5/8 in |
| Imperial | Utility brick | 11 5/8 in × 3 5/8 in × 3 5/8 in |
| Imperial | Concrete block | 8 in × 8 in × 16 in nominal |
| Metric | Brick | 190 × 90 × 57 mm |
| Metric | Brick | 215 × 102.5 × 65 mm |
| Metric | Brick | 230 × 110 × 76 mm |
| Metric | Concrete block | 390 × 190 × 190 mm |
Confirm the Actual Masonry Dimensions
Brick names and nominal concrete-block dimensions are useful descriptions, but manufacturer dimensions vary by product line and region. Confirm actual length, width and height before preparing the final takeoff. The width affects joint depth and mortar use even though wall-area calculations primarily use unit length and height.
Example: Mortar for a 20 ft × 8 ft Modular-Brick Wall
Assume a 20 ft long × 8 ft high net wall with no additional opening deductions, modular brick, a 3/8 in mortar joint, 80 lb mortar bags and 10% waste.
Net wall area: 20 ft × 8 ft = 160 sq ft.
Nominal modular-brick face: (7 5/8 in + 3/8 in) × (2 1/4 in + 3/8 in) = 8 in × 2 5/8 in = 21 sq in, or about 0.1458 sq ft.
Estimated bricks: 160 sq ft ÷ 0.1458 sq ft per brick ≈ 1,097.1 bricks.
Base mortar volume: 1,097.1 ÷ 1,000 × 19 cu ft per 1,000 modular bricks ≈ 20.85 cu ft.
Bags before waste: 20.85 cu ft ÷ 0.67 cu ft per 80 lb bag ≈ 31.1, so round up to 32 bags.
Waste-adjusted volume: 20.85 cu ft × 1.10 ≈ 22.93 cu ft.
Final bag estimate: 22.93 cu ft ÷ 0.67 cu ft per bag ≈ 34.2, so round up to 35 bags.
This is a planning example. Actual use varies with unit dimensions, joint width and depth, bond, wall thickness, openings, installer technique, dropped material and the yield of the selected mortar product.
Common Mortar Estimating Mistakes
Avoid these common problems when preparing a mortar takeoff:
- Ignoring waste from mortar boards, dropped material, tooling and cleanup
- Using the wrong joint thickness or ignoring joint depth and profile
- Selecting a brick name without confirming its actual manufacturer dimensions
- Forgetting to remove large doors, windows and other openings from gross wall area
- Mixing more mortar than can be placed within the product’s usable working time
- Using a generic bag yield instead of the yield printed by the manufacturer
- Assuming brick, block and stone-veneer installations all consume mortar at the same rate
Mortar Buying and Mixing Tips
Buy a modest amount above the calculated base quantity so normal job-site loss does not stop the work. Keep the estimate tied to the exact product because bag weight alone does not guarantee identical mixed yield.
- Keep unopened bags dry, raised off the ground and protected from weather
- Buy enough compatible mortar from the same product line when practical
- Mix only the quantity that can be placed within the manufacturer’s usable working time
- Follow the manufacturer’s water amount, mixing time and remixing instructions
- Do not use hardened, moisture-damaged or expired material
- Confirm mortar type, color and compatibility before starting visible work
Mortar Estimating Disclaimer
Use this guide and the Mortar Calculator as planning references only. Actual mortar requirements vary with unit dimensions, wall thickness, bond, joint width and depth, joint profile, openings, corners, leads, tooling, waste, weather, product yield and installer technique. Confirm mortar type, compatibility, water requirements, yield and final quantity with the manufacturer, masonry supplier, project specifications or mason. Structural and permitted masonry must follow approved plans and applicable code.
Get an instant estimate with the Mortar Calculator
Use the free Mortar Calculator to estimate bags of mortar, waste allowance and optional material cost before starting your masonry project.
Frequently Asked Questions
How many bags of mortar do I need?
Divide the waste-adjusted mortar volume by the mixed yield per bag and round up. For example, 22.93 cu ft divided by an approximate 0.67 cu ft per 80 lb bag equals about 34.2, so the purchase quantity is 35 bags.
How much mortar covers 100 square feet?
Coverage depends on masonry-unit dimensions, wall thickness, joint width and depth, bond and bag yield. Using the calculator’s modular-brick planning rate with a 3/8 in joint, 100 sq ft is roughly 13 cu ft of mortar before waste, but confirm against the selected product and wall details.
Should I add waste to a mortar estimate?
Yes. A 5% to 15% allowance can cover mortar-board loss, dropped material, tooling, cleanup and normal variation. Ten percent is a practical planning starting point, but actual conditions may require a different allowance.
Can I use mortar for concrete?
Do not treat mortar as a general substitute for concrete. Mortar is formulated for masonry bonding and joints, while concrete is formulated for structural masses such as slabs and footings. Use the product specified for the application.
What is the difference between mortar and concrete?
Mortar normally uses cementitious binder, fine aggregate and water to bond masonry units. Concrete generally also contains coarse aggregate and is placed to form slabs, footings and other masses. Their mix designs, performance and intended uses differ.
How thick should mortar joints be?
Common planning sizes include 3/8 in or 1/2 in and 10 mm or 12 mm. The correct joint depends on unit tolerances, appearance, exposure and project specifications, so follow the plans and manufacturer guidance.
Can I estimate mortar for concrete block walls?
Yes. Use the actual block dimensions, specified bedding method, joint size, net wall area and product yield. Fully bedded and face-shell-bedded construction can consume different quantities.
How accurate is the Mortar Calculator?
It provides a practical planning estimate from typical unit rates and bag yields. Actual usage changes with joint geometry, wall configuration, workmanship and product yield, so confirm the final order before purchasing.
Does the calculator account for doors and windows?
The calculator treats the entered wall dimensions as net wall area. Calculate rectangular wall sections around openings or subtract opening area before using the final quantity.
Can mortar be used for stone veneer?
Many stone-veneer systems use a mortar or manufacturer-specific setting material, but coverage and installation details differ from brick and block. Follow the veneer manufacturer’s approved system and product yield rather than relying on a brick rate.