Mortar Calculator

How to calculate how much mortar you need

Mortar is sold in bags, and the bag label or data sheet says how many bricks or blocks one bag lays. So the calculation has two steps. First you count the bricks or blocks, then you divide by the yield of one bag.

The pieces per square foot are geometry. A standard 8 × 16 inch block face covers 8/9 of a square foot, so a square foot takes 1.125 blocks, as the CMHA Tech Note 04-02A explains. For brick, the Brick Industry Association lists the quantities below in its Technical Note 10, without waste and with a 3/8 inch joint (checked October 2026).

How many bricks or blocks does an 80 lb bag lay?

This is the number that moves the result most. SPEC MIX, a maker of preblended mortar, publishes the yield of its 80 lb bags for each piece. Its table is the same for the masonry cement mix (data sheet) and the mortar cement mix (data sheet), and different for the portland lime and sand mix (data sheet). Both were checked in October 2026. SPEC MIX says the yields are approximate, depend on labor practices, site conditions and design of work, and include typical waste. It also notes that some areas, such as FL, CA, OR and WA, experience higher yields and tells buyers to ask a local representative. The calculator does not adjust for region.

Two other sources give a single figure. The QUIKRETE Mortar Mix data sheet says an 80 lb bag lays up to 13 standard 8 × 8 × 16 inch blocks. It also says up to 37 standard bricks, but it does not define a standard brick, so the calculator does not apply that number to any brick size. The CMHA Tech Note gives a rule of thumb of 16 conventional blocks per 80 lb bag of preblended mortar. Its table says the values include nominal waste and assume the mortar goes only on the face shells of the block. The SPEC MIX web page for its masonry cement mix lists higher brick yields than its PDF data sheet (40 to 45 modular bricks instead of 39 to 41, checked October 2026). The block yields are the same in both. The calculator uses the PDF because its lower brick yield asks for more bags, which is the cautious choice. Pick the source in the “Mortar product” list and compare.

Example: a block wall with a door

A wall is 20 ft long and 8 ft high and has one 3 ft by 7 ft door. It is built with 8 inch concrete blocks and SPEC MIX masonry cement and sand mortar, which lays 11 to 13 of them per 80 lb bag. The calculator opens with the wall already typed, so type 21 in the doors and windows box to get these figures.

So the job needs between 13 and 15 bags, and 15 is the safe number to take to the store. The concrete block calculator counts the blocks of a wall with several sections and adds the grout, and the brick calculator does the same for brick. Both can give you a count to type in the Count tab here. Their mortar lines use other figures, so the numbers will not match this page. The concrete block calculator uses the CMHA rule for masonry cement, about 30 blocks per 70 lb bag. That bag is cement only and is mixed on site with masonry sand, so it shows fewer bags plus a ton of sand. The brick calculator uses the QUIKRETE figure of up to 37 standard bricks per 80 lb bag for every brick size. This page uses 80 lb bags of preblended mortar, which already contain the sand, with a yield for each brick or block size.

Bags of mortar for common wall sizes

The table uses SPEC MIX masonry cement and sand mortar, walls without openings, 8 inch concrete block and modular brick. Each bag cell is the range from the high end to the low end of the yield, so the larger number is the cautious one.

Mortar for repointing brick

Repointing, also called tuckpointing, replaces old mortar in the joints. The mortar needed depends on how wide the joint is and how deep it is ground out, not on the number of bricks. SPEC MIX publishes how many square feet of modular brick wall one 80 lb bag of its Tuckpoint Mortar covers (checked October 2026). The Repointing tab uses this table.

A 100 square foot wall with 3/8 inch joints ground out 1/2 inch deep takes 100 ÷ 85 = 1.18 bags at the low end and 100 ÷ 95 = 1.05 at the high end, so 2 bags either way. The coverage is for modular brick only.

Mortar for stone and other jobs by volume

When the job is a mortar bed, a stone veneer or a stone wall, you need a volume, not a count of pieces. Multiply the length, the width and the thickness in feet, then divide by the cubic feet of wet mortar one bag makes. SPEC MIX says an 80 lb bag of its Building Stone Mortar produces about 0.75 cubic feet, and that the square foot yield depends on the cut of the stone and the joint profile.

For example, a 10 ft by 10 ft area with a 2 inch bed is 10 × 10 × (2 ÷ 12) = 16.67 cubic feet. Divided by 0.75 that is 22.2, so you need 23 bags, which weigh 1,840 lb. The thickness you use is your decision or your installer’s, so measure it on the real job. If your bag shows a different yield, choose “My own yield”.

How much extra mortar to buy

The SPEC MIX and CMHA yields include a typical amount of waste, so the calculator adds nothing unless you ask. The Brick Industry Association works from the theoretical volume of mortar in the wall, and for that figure it says that as a general rule you add 15 to 25 percent. Particular job conditions or experience can change that. If you want a margin, type it in the extra box and the calculator adds it to the number of pieces before it divides.

Tips for ordering

• Read the label. The pieces per bag, the bag weight and the mortar type change from product to product.
• Use the low end of the yield range when you do not want to run out in the middle of a course.
• The mortar type (M, S or N) is chosen by the project plans or the mason. SPEC MIX lists one yield table for types M, S and N of each mix.
• Mortar for brick and block is not concrete. For concrete slabs, footings and posts, use the concrete calculator. For the cement itself, see the cement calculator.
• Tile adhesive is a different material. The thinset calculator works from the trowel size and the coverage of the bag.

Frequently asked questions