Count the masonry units
Start with the brick, block, or other unit quantity for the portion of work that will use the same mortar and joint conditions.
Concrete & masonry
Mortar Calculator
Calculate how much mortar you need for brick, block, or other masonry work. Use a product-specific units-per-bag yield for the safest purchasing estimate, or estimate theoretical joint volume from unit and mortar-joint dimensions.
Calculation guide
How much mortar do you need?
The most dependable purchasing method is to start with the yield published for the exact mortar product and masonry unit. If no usable units-per-bag coverage is available, the detailed method can estimate the theoretical volume of regular head and bed joints before you apply your own allowance and product yield.
Use product yield when possible
Manufacturer and supplier yields account more directly for the product and intended unit than a universal bag rule. Enter that units-per-bag figure in Quick Yield.
Model joints only when needed
Detailed Geometry estimates the rectangular mortar volume around a repeating unit module. It is useful for planning, but real masonry joints and bedding can differ.
Round purchasing up
After allowance and product yield are applied, mortar bags are rounded up because partial bags are generally not a purchasing unit.
Quick Yield formula
Planned units = unit count x (1 + allowance / 100)
Bags to buy = ceil(planned units / units per bag)
This method is intentionally simple because the most important variable - product coverage - comes from the mortar manufacturer, supplier, or project data rather than from a universal assumption built into the calculator.
Detailed joint-volume formula
The calculator assigns one head-joint strip and one bed-joint strip to each repeating masonry module. Their overlap is counted once by subtracting the exposed unit face from the full module face.
Module face = (unit length + head joint) x (unit height + bed joint)
Joint face per unit = module face - unit face
Mortar volume per unit = joint face x installed joint depth
This is a theoretical rectangular-joint model. Boundary courses, tooling, voids, frogs, cores, shell bedding, furrowing, squeeze-out, workmanship, and field loss can all change actual mortar usage.
Worked example
Suppose a project uses 500 modular-face bricksmeasuring 7.625 x 2.25 in, with3/8-in head and bed joints and a theoretical3.625-in installed joint depth.
The repeating module is 8 x 2.625 in. The unit face is 17.15625 in2 and the module face is 21 in2, leaving 3.84375 in2 of theoretical joint face per unit. At 3.625 in deep, that is about 13.9336 in3 of mortar per unit.
500 units -> about 4.032 ft3 of theoretical mortar
With a 10% allowance, the planned amount is about4.435 ft3. If the exact mortar product states a mixed yield of 0.70 ft3 per bag, the estimate is about 6.34 bags, so you would plan to buy 7 whole bags.
Quick Yield vs. Detailed Geometry
Use Quick Yield when
- The product gives units laid per bag.
- Your unit size and joint conditions match that guidance.
- You want the safest direct purchasing estimate.
Use Detailed Geometry when
- You need a theoretical joint-volume estimate.
- You know the actual unit and joint dimensions.
- You can supply a product-specific mixed yield for bag conversion.
Why mortar coverage varies
Mortar use is not fixed by bag weight alone. Coverage can change with brick or block size, head and bed joint thickness, installed joint depth, bedding method, mortar consistency, unit absorption, workmanship, waste, and the product's actual mixed yield.
This is why HomeMeasureWorks does not silently assume that every 80-lb bag lays the same number of bricks or blocks. When the exact product publishes a yield for your masonry unit, use that figure.
Brick joints and block bedding are not always equivalent
A full-depth rectangular model can be a reasonable planning approximation for conventional fully filled brick joints, but hollow concrete masonry may be laid with mortar on face shells rather than across the full block depth. Other unit shapes and installation methods can also depart from the model.
For those cases, Quick Yield is usually the better method when product or project coverage information is available. Do not use the calculator to decide how a structural masonry joint should be constructed.
How much extra mortar should you allow?
There is no single allowance that is correct for every project. The preset buttons are planning conveniences, not rules. Choose an allowance that reflects the reliability of your yield data, project geometry, handling, expected waste, and field conditions.
If project documents, the supplier, or the mortar manufacturer specifies a quantity or allowance, follow that project-specific guidance instead of a generic preset.
Mortar calculator FAQ
How many bags of mortar do I need?
Divide your planned masonry-unit count by the number of those units one bag is expected to lay, then round up. If you work from joint volume instead, divide the planned mortar volume by the mixed yield of one bag.
How many bricks does one bag of mortar lay?
There is no universal number. It depends on brick size, joint dimensions, mortar product, bedding, workmanship, and field conditions. Use the coverage supplied for the exact product and brick when possible.
Can I use this for concrete block?
Yes, especially in Quick Yield mode when you have a product-specific blocks-per-bag figure. Detailed Geometry requires caution because hollow CMU may use shell bedding rather than a full-depth joint.
What is installed joint depth?
It is the depth of mortar that actually occupies the head and bed joint in the wall model. It should not be automatically assumed to equal the full depth of every masonry unit.
Why are head and bed joints separate?
Vertical head joints and horizontal bed joints can have different planned thicknesses. Keeping them separate makes the geometric estimate more transparent.
Does bag weight tell me the mortar yield?
No. Bag weight is not a substitute for mixed yield. Use the product's stated mixed volume or unit coverage. The optional bag-weight field here only totals the dry package weight you would purchase.
Does the calculator choose Type N, S, M, or O mortar?
No. Mortar selection depends on the application, project requirements, materials, exposure, and design. This page estimates quantity only.
Should I always add 10% extra mortar?
No. Ten percent is only a convenient preset. Use the allowance appropriate to your product guidance, measurements, workmanship, and project conditions.
Can I calculate mortar cost?
Yes. Enter the optional price per bag. Cost is based on the whole number of bags the calculator says to buy.
Can I switch between Imperial and Metric units?
Yes. Detailed joint dimensions and optional bag weight are converted when you switch measurement systems. The calculation engine keeps a consistent internal basis.
Can I share or save the calculation?
Yes. A valid calculation is stored in the page URL. Copy or share that URL and reopen it later to restore the saved inputs and result.
Assumptions and limitations
Quick Yield assumes the units-per-bag value you enter is applicable to the exact mortar, masonry unit, joint size, and installation conditions. Detailed Geometry treats the masonry as a repeating rectangular module and estimates the idealized volume of head and bed joints at the depth entered.
The detailed model does not explicitly simulate wall edges, bond patterns, partial units, frogs, cores, shell bedding, furrowed beds, tooling profiles, squeeze-out, mortar dropped during installation, varying joint thickness, or site-specific workmanship. Your allowance is applied after the base estimate.
This calculator estimates material quantity only. It does not select mortar type or proportions, determine masonry strength, specify joint construction, calculate structural capacity, or replace project documents, codes, manufacturer instructions, or professional design requirements.