Mortar Calculator

Pre-mixed mortar is sold by the bag, and each bag is rated for a set number of bricks or blocks. That rating comes from the maker's data sheet and leaves out waste. The calculator adds the waste you set and rounds up to whole bags. Treat the result as an estimate, since yields vary by product and by joint thickness.

How to use this calculator

1. Pick the laying: modular brick or standard concrete block. A block covers far more wall than a brick, so the bag counts differ a lot.
2. Measure the wall's length and its height from the base to the top course, in feet. For a sloped top, such as a gable, use an average height.
3. Open More options and enter the area of every door and window, in square feet. Leave it at zero for a solid wall.
4. Keep the extra for waste at 15 percent, the low end of the brick industry's range. Raise it for thick beds or full-bed block work, which use more mortar.
5. Check the bag's data sheet. If its yield differs from the one used here, add the waste to the units, divide by that yield and round up. Buy all the bags before the first course goes down.

Worked examples

Mortar bags for common wall sizes, brick and block

Each cell: Mortar mix (80 lb bags). Inputs not in the table use the calculator's starting values.

How the bag count is worked out

The calculator takes the wall area, which is length times height minus any openings. For brick, it multiplies that area by 6.75 bricks per square foot to get the bricks in the wall. For block, it divides the area by the face one block covers, 0.889 sq ft, which includes its joint. It then adds the waste to the unit count and divides by the number one bag lays. Makers' data sheets give 35 to 37 bricks standard bricks or 12 to 13 blocks concrete blocks per bag. The calculator uses the lower figure in each range, so it errs toward more bags.

The extra covers mortar that is mixed but not placed, and mortar lost on the way to the wall. The calculator counts bags rather than cubic feet, because pre-mixed mortar is sold by the bag and makers rate each bag by the units it lays.

Type N, Type S and mixing your own

The types you will see most often are Type N and Type S. Type N is the general-purpose mortar for most walls above ground. Type S is stronger and suits structural walls, including walls that carry loads or hold back soil. Check the wall designer's plans or local code for the type the job needs.

If you mix your own from masonry cement and sand, follow the mix proportions printed on the bag. The bag count here is for pre-mixed mortar, so it does not tell you how much sand to buy.

Bricks, blocks and what the count leaves out

The brick and block counts here are the units in the wall, without breakage, so the number to buy is higher. Work out the purchase with the brick calculator or the block calculator, and use this page for the mortar.

A block covers far more wall than a brick, so a block wall takes fewer bags for the same area.

Mistakes to avoid

• Setting the waste to zero. The yields leave out waste, so a zero allowance can leave you short.
• Treating a thick bed like a standard one. Thicker joints and full-bed block work use more mortar.
• Leaving openings in the count. A large door or window adds units you will never lay.
• Mixing more mortar than you can place. Pre-mixed mortar stiffens once water is added, so mix only what you can lay within the working time on the bag.

How much mortar do I need by volume?

If you mix your own, work in cubic feet. A block wall takes about 8.5 cubic feet of mortar for every hundred square feet of wall, waste included. A brick wall takes about 8.1 cubic feet for every thousand modular bricks, before waste, so add 15 percent or more on top.

Common questions