Mortar Calculator

How to calculate how much mortar you need

Mortar is estimated from the number of units you lay, not from the wall’s volume. The QUIKRETE Mortar Mix data sheet states that each 80 lb (36.2 kg) bag lays up to 13 standard 8 × 8 × 16 in blocks or up to 37 standard bricks. Divide your count by that yield and round up.

80 lb bags = number of blocks ÷ 13 (rounded up)
80 lb bags = number of bricks ÷ 37 (rounded up)

The calculator above does this and adds a waste allowance, 10% by default. It also shows the total dry weight so you can plan how to move the bags.

1. Count the blocks or bricks. If you only have wall dimensions, get the block count from the concrete block calculator first, or the brick count and BIA mortar volume from the brick calculator. This page starts from that count.
2. Pick the unit. Standard 8 × 8 × 16 in block, or standard brick.
3. Set a waste allowance. 10% covers mortar dropped from the board, mixed batches that stiffen before you use them, and cut units at corners.
4. Round up to whole bags. You cannot buy part of a bag, and a short last course is the worst time to run out.

How many bags of mortar for common block and brick counts?

This table answers the counts people search for most. Bags are 80 lb mortar mix at QUIKRETE’s published yield of up to 13 blocks or 37 bricks per bag. Every figure comes from the site’s calculation library.

The “up to” in the data sheet matters: treat 13 blocks or 37 bricks per 80 lb bag as a maximum. Real counts drop with wider joints, wavy courses, mortar left on the board and cut units. The 10% allowance covers normal losses; a first-time mason may want more.

How much mortar for a block wall by size?

If you know the wall size rather than the block count, convert first. A standard 8 × 16 in block face covers 0.89 ft², which is 1.125 blocks per square foot of wall. The full block count, including openings and courses, belongs on the concrete block calculator; this table carries those counts through to mortar.

As a rule of thumb from the same numbers, one 80 lb bag covers about 11.6 ft² of 8 × 16 in block wall (13 blocks ÷ 1.125 blocks per ft²). The table has no brick column by wall area because brick sizes and bond patterns vary too much for one per-square-foot figure; count your bricks and use the brick setting.

What type of mortar is in a bag of mortar mix?

QUIKRETE Mortar Mix in its standard formulation meets ASTM C270 and ASTM C1714 as Type N mortar, according to the data sheet. Other types are available from QUIKRETE by special request. ASTM C270 is the standard specification for mortar for unit masonry, and it sets minimum properties for each type.

The figures are the property requirements reproduced in QUIKRETE’s data sheet. The data sheet refers readers to Appendix X1 of ASTM C270 for help choosing a type. Which type a wall needs is a design decision for your plans, engineer or local building department, not something a calculator can settle. Stronger is not automatically better; this page counts bags of whichever type is specified.

How much water does mortar mix need?

Start with about 5 quarts (4.7 L) of clean water for each 80 lb bag, or 3 3/4 quarts (3.5 L) for a 60 lb bag, per the QUIKRETE data sheet. Pour the dry mix into the water, not the other way round, and mix for at least 5 minutes by hand or in a paddle mixer.

Add more water only in small amounts. The data sheet expects the maximum to stay below 6 quarts (5.7 L) for an 80 lb bag and 4 1/2 quarts (4.3 L) for a 60 lb bag. The test for the right consistency is practical: a 1/2 in layer of mortar should not slide off the trowel when you hold it nearly vertical.

For a 16-bag job like the 20 × 8 ft wall above, that is about 80 quarts, or 20 gallons, of mixing water at the starting rate. Have a hose or several full buckets on site before you open the first bag.

How thick should mortar joints be?

QUIKRETE’s application directions call for a full bed of mortar about 1/2 to 3/4 in (13 to 19 mm) thick under the block. Press each block down into the bed and sideways against the last one with a slight twist, then tool the joints when the mortar is thumbprint hard to make them watertight and smooth.

Joint thickness drives mortar use more than anything else. The published yield is an “up to” figure; a mason running thick beds to correct an uneven footing can easily lay fewer than 13 blocks per bag. If your first course needs a thick leveling bed, buy an extra bag or two for it alone.

In very hot, dry or windy weather, the data sheet says to cure the mortar with a gentle mist of water so it does not dry too fast. Otherwise masonry mortar does not need special curing.

Smaller bag sizes: 60, 40 and 10 lb

QUIKRETE lists Mortar Mix in 10, 40, 60 and 80 lb bags and a 30 kg bag, but publishes its yield only for the 80 lb bag. Scaling that yield by weight gives a working estimate for the smaller bags. Treat these as estimates, round up and keep a spare bag.

The 10 lb bag is meant for repairs and tuckpointing a few joints, not for laying a wall. For any new wall the 80 lb bag is the size to price, and the calculator counts in 80 lb bags for that reason.

Why bricks and blocks use such different amounts of mortar

One bag lays up to 37 bricks but only 13 blocks, which looks backwards until you compare the wall area. A standard 8 × 16 in block covers 0.89 ft² of wall face, so 13 blocks cover about 11.6 ft². Bricks have a much smaller face than an 8 × 16 in block, so 37 bricks cover a very different wall area than 13 blocks. How much depends on the brick size and bond, and the data sheet gives yield per unit only, so work from your brick count rather than from wall area.

That is why the calculator works from the unit count rather than the wall area: the published yield is per unit. It also means two walls of the same size can need very different amounts of mortar.

For planning, count the bricks carefully, including headers, soldiers and any rows laid on edge, and size the mortar from that count.

Planning mortar for a whole block wall

A block wall is three separate orders: the poured footing, the blocks and the mortar. Working them in order keeps each number honest, because each one starts from the result of the step before.

1. Footing. Size the concrete for the footing on the concrete footing calculator, following the footing width and depth in your plans.
2. Blocks. Count the blocks for the wall on the concrete block calculator, subtracting doors and windows.
3. Mortar. Enter that block count here, add your waste allowance and round up to whole bags.
4. Water and handling. Multiply the bag count by about 5 quarts of water and by 80 lb of weight so you know what the job needs on site.

Take a 30 × 6 ft garden wall as an example. It takes 203 standard blocks. At up to 13 blocks per 80 lb bag that is 16 bags, or 18 with 10% extra. Eighteen bags weigh 1,440 lb dry and need about 90 quarts, or 22.5 gallons, of mixing water at the starting rate on the data sheet.

Buy the mortar after the block count is final. If the design changes, such as a taller wall or an added pier, recount the blocks first and then rerun this calculator, rather than adjusting the bag count by eye.

Store bags off the ground and under cover until you use them. QUIKRETE describes Mortar Mix as a pre-blended, sanded product that is mixed only with clean water, so keep the bags dry until you open them. Open bags only as you need them, and keep the next day’s bags sealed.

Common mistakes when buying mortar

Most mortar shortfalls come from treating the yield as a guarantee or from skipping steps between the wall and the bag count.

• Reading “up to” as exact. 13 blocks per bag is the data sheet’s maximum. Without an allowance, 100 blocks at 8 bags leaves no margin for a dropped batch.
• Using the block yield for bricks, or the reverse. 100 bricks need 3 bags; 100 blocks need 8. Pick the right unit before you trust the number.
• Estimating from wall area by guesswork. Convert area to a block count first: a 20 × 4 ft wall is 90 blocks, not “about 80”. Openings and partial blocks are handled on the concrete block calculator.
• Counting grout or core fill as mortar. Mortar bags lay the units. Filling block cores with concrete is a separate volume calculation on the block calculator.
• Adding water to stiffened mortar late in the batch. Mix smaller batches instead. A bag thrown away because it set on the board is part of the waste you planned for.
• Using the wrong bag size in the math. The published yield is for 80 lb bags. If you buy 60 lb bags, the count goes up by about a third.

Mortar calculator vs block, concrete mix and QUIKRETE calculators: which one to use

This page turns a block or brick count into bags of mortar mix. Other parts of the same job have their own tools:

• Concrete block calculator: how many 8 × 8 × 16 in blocks a wall needs, openings included, and core fill.
• Concrete wall calculator: if you are pouring a solid concrete wall instead of laying block.
• Concrete mix ratio calculator: mixing concrete from cement, sand and stone rather than using premix.
• QUIKRETE calculator: bags of QUIKRETE concrete mix for slabs, posts and footings.
• Concrete footing calculator: the poured footing a block wall sits on.