Mortar Calculator

How to use this calculator

1. Pick block or brick. The coverage per bag is completely different.
2. Enter the unit count if you have it. Masons estimate mortar from unit count, not from area.
3. No count yet? Enter the wall area instead and it converts at 1.125 block or 6.75 brick per square foot.
4. Choose what you are buying. Preblended bags and masonry cement are priced and counted differently.
5. Keep the waste allowance on. Mortar gets dropped, and a stiffened board gets thrown away.

Need the block count first? The concrete block calculator takes wall dimensions and returns blocks, courses and an approximate mortar figure.

The two different bags called mortar

This is the thing that causes most of the confusion, and it produces roughly double errors when people get it wrong.

Preblended mortar mix is cement and sand already combined in an 80, 60 or 40 lb bag. You add water only. Sakrete Mortar Mix and Quikrete Mason Mix are this. An 80 lb bag lays around a dozen block.

Masonry cement comes in roughly 70 lb bags and contains no sand. The mason adds 2 1/4 to 3 cubic feet of sand per bag on site. When a masonry supplier says "three bags per hundred block," this is the bag they mean, and one of these goes much further than a bag of preblend.

So the same wall is about 15 bags of 80 lb preblend, or about 6 bags of masonry cement plus roughly a ton of sand. Both are right. They are different products.

Mortar coverage per bag

These are Sakrete's published figures, from the Type S and Type N data sheets, and they are the most complete set because Sakrete publishes all three bag sizes.

Other manufacturers are close but not identical, so expect a bag either way on a big job. Quikrete Mason Mix states an 80 lb bag lays up to 13 block or 37 brick, and Spec Mix publishes 11 to 13 block and 40 to 45 modular brick. The range across the industry is 11 to 13 block per 80 lb bag, so this calculator uses 12.

By volume, an 80 lb bag makes roughly 0.7 to 0.75 cubic feet of wet mortar. Sakrete does not publish a cubic foot yield for its mortars at all, which is why coverage is quoted in units laid rather than volume.

The masonry cement rule of thumb

If you are buying masonry cement and sand, the trade uses round numbers:

• Block: 2 1/4 to 3 bags per 100 block. Suppliers disagree, so this calculator uses 3, the most common figure.
• Brick: 7 bags per 1,000 brick, which is close to unanimous across suppliers.
• Sand: about 1 ton per 7 bags of mortar, or 2 1/4 to 3 cubic feet of damp sand per bag.

Worth knowing where these come from: they are regional masonry supplier estimating guides, not an industry standard. Neither the Concrete Masonry and Hardscapes Association nor the Brick Industry Association publishes a bags-per-100-block rule. They are reliable because every supplier arrives at nearly the same number, not because a standards body blessed them.

The rule of thumb is also more generous than the per-bag coverage math, because it is built on real jobs with real waste. If the two numbers disagree, the supplier's rule is the safer one to order against.

Type N, Type S and Type M

Mortar type is about strength, not quantity, and the quantity math above applies to all of them.

The counterintuitive part is that stronger is not better. The Brick Industry Association advises selecting the mortar type with the lowest compressive strength that meets the project requirements, because a mortar much stronger than the units it joins concentrates stress in the units instead of the joints. Type N is the default for most above-grade residential work.

Code sometimes decides for you. The Concrete Masonry and Hardscapes Association notes that empirically designed foundation walls require Type M or S, and seismic design categories D, E and F require Type S or M.

One correction on those strengths, because it changes what they mean. ASTM C270 lets you specify mortar two mutually exclusive ways, and the strengths in the table belong to only one of them. PCA states the rule plainly: "Mortar types are to be identified by either proportion or property specifications, but not by both." The strengths above are the property specification, and they apply to mortar "proportioned, mixed and conditioned in the testing laboratory" at a flow of 110 plus or minus 5 percent, per CMHA TEK 18-05B. Nobody mixing on site is working to that. A DIYer, and most masons, work to the proportion specification, which is a recipe and carries no strength claim at all. So "Type S mortar" mixed in a tub means "the Type S recipe," not "1,800 psi mortar." Those are different statements and C270 does not let you infer one from the other.

It matters in one practical situation. If mortar from your job is sampled and tested, the result will come back well below the table, and that is expected rather than a failure. CMHA is blunt about it: "Field mortar compressive strength test results should never be compared to the requirements in ASTM C270 Table 2, which apply to laboratory-prepared mortar only." The reason is almost the opposite of what you would guess. Mortar in a finished joint ends up stronger than a test cylinder from the same batch, because the units absorb water out of the joint and drop its water to cement ratio, while a cylinder cast in a non-absorbent mold keeps all of its water.

If you are mixing from scratch rather than buying preblend, the classic proportions by volume are 1 part cement to 1 part lime to 6 parts sand for Type N, and 1 to 1/2 to 4 1/2 for Type S, per the National Lime Association. Those are worth understanding as examples rather than as the standard, which the next section explains. Our mix calculator handles ratio-based batching.

How to mix mortar

Two routes: a preblended bag where you add only water, or cement plus your own sand.

From a preblended bag

Water first, then the bag, then mix for at least five minutes. The manufacturers' figures:

On yield, be careful what you read. Neither Quikrete nor Sakrete publishes a cubic-foot yield for their bagged mortars; they publish units laid, and an 80 lb bag lays about 12 or 13 standard blocks, or 35 to 37 standard bricks. Working backwards from their own cement-plus-sand coverage figures, an 80 lb bag makes roughly 0.6 to 0.7 cubic feet. You will find 0.88 cubic feet quoted by one manufacturer, and it does not reconcile with anybody's coverage numbers, so treat it with suspicion.

From cement and sand

The ratio rule in C270 is not a fixed recipe, which is the thing almost every page gets wrong. Sand is specified as a range: "not less than 2-1/4 and not more than 3 times the sum of the separate volumes of cementitious materials," measured damp and loose. The cementitious side for portland and lime is 1 part portland to 1/4 lime for Type M, over 1/4 to 1/2 for Type S, over 1/2 to 1-1/4 for Type N, and over 1-1/4 to 2-1/2 for Type O.

Run that for Type N at 1 portland to 1 lime and you have 2 parts cementitious, so sand is anywhere from 4-1/2 to 6 parts. Which is where the folk recipe 1:1:6 comes from. It is one legal point inside C270's range, not the specification itself. Same for the 1:1/2:4-1/2 that gets quoted for Type S. Both are fine. Neither is "the ASTM ratio," and a page presenting them that way has misread the standard.

With a bag of masonry or mortar cement the arithmetic is easier, because the trade treats one bag as one cubic foot: one bag of Type S masonry cement to 2-1/4 to 3 cubic feet of damp loose sand gives Type S mortar. Quikrete's Type S masonry cement sheet says "mix 1 part QUIKRETE Masonry Cement with 2.25 to 3 parts masonry sand," and one 70 lb bag with 240 lb of sand makes about 2.75 cubic feet, enough for roughly 46 blocks or 144 bricks.

Mixing time is a real requirement, not a suggestion. Three to five minutes in a mechanical mixer after every ingredient is in, per TMS 602 as reproduced in the federal UFGS 04 20 00 unit masonry specification: "mix cementitious materials and aggregates between 3 and 5 minutes in a mechanical batch mixer." CMHA gives the reason: mixed too briefly, "the mortar mixture may not attain the uniformity necessary for the desired performance." Bagged products ask for a minimum of five minutes, which satisfies it.

Use the right sand

Mortar sand must meet ASTM C144, which is a different gradation from the ASTM C33 concrete sand you would use in concrete. C144 requires everything to pass the No. 4 sieve and 95 to 100 percent to pass the No. 8. Concrete sand fails from the coarse end and play sand fails from the fine end, being graded to a cosmetic spec with too little of the mid-range material the standard calls for. Neither is forbidden by name in any document we could find, but both fall outside the envelope, and the consequence is the same: harsh mortar that will not hold water or spread.

Sand is specified damp and loose for a reason. Surface moisture holds the grains apart, so the same weight of sand takes up more space damp than dry. Measure dry sand by the shovel and you put in more sand than the recipe calls for, which makes the mortar lean and harsh. PCA gives the conversion that makes this manageable: one cubic foot of masonry sand by damp loose volume is reckoned equal to 80 lb of dry sand, with damp sands typically carrying 4 to 8 percent moisture. No US masonry standard publishes a single bulking percentage, because it depends on the sand, so the tidy "sand bulks 20 to 30 percent" figure you will find is from Indian Standard literature rather than ASTM.

Board life, and why you can add water to mortar but not concrete

This is the most useful thing on the page if you have ever been told never to add water to a mix.

Mortar has a board life of 2-1/2 hours from initial mixing, or 2 hours in hot weather. The federal masonry specification puts both conditions in one sentence: "discard mortar that has begun to stiffen or is not used within 2-1/2 hours after initial mixing." Two tests, and whichever comes first wins. CMHA, BIA and PCA all publish the same 2-1/2 hours. Note that at least one manufacturer is stricter for its own product: Sakrete's Type S masonry cement sheet says to use the mortar within one hour, and a product instruction beats a general rule.

Retempering is allowed. Adding water to mortar that has stiffened on the board is not a bodge, it is standard practice. The Brick Industry Association goes further than permitting it: "the addition of water to mortar (retempering) to replace water lost by evaporation should be encouraged, when necessary." CMHA agrees that "retempering is permitted to replace water lost by evaporation."

The limit is why it stiffened, and it is the whole rule in one line. Water lost to evaporation can be replaced. Stiffening from hydration, meaning the cement has started to set, cannot be chased with water, and CMHA says such mortar "should be discarded if it shows signs of hardening." Within the first couple of hours on a board in the sun it is evaporation. If it is going off, it is over.

So why is this the opposite of the concrete rule? Because the two materials are specified on different things. Concrete is specified on a water to cement ratio that governs a structural member, so NRMCA CIP 26 permits one bounded adjustment before any significant discharge, must not exceed the specified ratio, and allows nothing at all once about a quarter yard has come out of the truck. Mortar is specified on proportions and judged on bond, workability and water retention rather than on a ratio, so repeated retempering across the board life is acceptable. The thing both materials forbid is identical: adding water to something that has begun to set.

One honest disagreement to flag, because it is a real one. Sakrete's mortar mix data sheets state flatly that "re-tempering impairs performance," with no evaporation or hydration distinction. That contradicts BIA, PCA, CMHA and TMS 602. It is also a defensible position for a bagged product aimed at people more likely to over-water than a working mason. Follow your bag.

Three things not to put in mortar

Antifreeze. This one is documented rather than folklore. BIA Technical Note 1 says "do not use antifreeze compounds," on the grounds that at usable doses they do not meaningfully lower the freezing point and they cause significant loss of both compressive and bond strength. CMHA is stronger: antifreezes "are not recommended for use in mortars and are prohibited for use in grouts." The correct cold weather move is heat, not chemistry. Below 40 degrees, heat the mixing water or sand to produce mortar between 40 and 120 degrees and cover the finished work.

Dish soap. Masons have used a squirt of detergent as a cheap plasticiser for generations, and it works by entraining air. No standard names it, so this is not a quotable prohibition, but the rule that covers it is: PCA states that admixtures "should not be used in masonry mortar unless specified," and where specified must meet ASTM C1384. Soap meets no standard and entrains an unknown amount of air, and air content is precisely the variable the standards go out of their way to cap, because bubbles at the interface between mortar and unit reduce bond.

Extra portland cement, to make it stronger. The blunt version of this rule is itself wrong, so here is the accurate one. C270 genuinely does permit blending portland cement with Type N masonry or mortar cement to reach Type S or Type M; that is a row in its own table. What is wrong is adding portland to a bag that is already Type S or Type M, which lands outside the standard entirely, and adding it by eye, which changes the cementitious volume and silently breaks the 2-1/4 to 3 sand ratio at the same time. We could not find a published sentence in any ASTM standard, CMHA document, BIA note, PCA publication or manufacturer data sheet forbidding it, so treat this as trade practice with a good reason behind it rather than a documented rule.

And the reason not to reach for strength at all is sourced. BIA puts it as directly as it can: "stronger is not necessarily better when specifying mortar. In fact, the opposite is often true," with the advice to "select a mortar Type with the lowest compressive strength meeting the project requirements." PCA adds that the payoff is poor anyway, since a stronger mortar raises assembly strength by much less than proportionally.

Joint thickness

Every coverage figure on this page assumes a 3/8 inch joint, which is the US standard and is built into the unit sizes themselves. A nominal 8 by 8 by 16 inch block actually measures 7 5/8 by 7 5/8 by 15 5/8, so the block plus its joint equals the 8 inch module.

Thicker joints use meaningfully more mortar, and no manufacturer or association publishes a multiplier for it. If you are working to wider joints, treat the bag count as a floor rather than an estimate and buy accordingly.

Related tools

Count the units first with the concrete block calculator, fill the block cores with the same tool, and price the bags with the Sakrete or Quikrete calculators. If you are pouring a footing under the wall, use the footing calculator. Both Quikrete mortar products and which is Type N or Type S are covered in Quikrete mix types.