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Mortar Calculator

Count the bags of premixed mortar needed to lay a given number of bricks and concrete blocks, using the yield per bag and a waste allowance.

Level: Grades 6–7

  • Common Core standard 6.RP.A.3.bSolve unit rate problems including those involving unit pricing and constant speed.
  • Common Core standard 7.RP.A.3Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.
Printable worksheet

Mortar Calculator

Inputs

Enter 0 if you are laying only block.

Enter 0 if you are laying only brick.

About 37 standard bricks per 80 lb bag of premixed mortar. Check your bag.

About 13 standard blocks per 80 lb bag. Check your bag.

Mortar dropped, stiffened in the tub or used for thicker joints.

Used for the total weight. For a smaller bag, lower the bricks and blocks per bag to match.

Result

Bags of mortar mix

24 bags

Buy 24 bags of 80 lb mortar mix, about 1,920 lb in all.

Bags before rounding (with waste)
23.33
Bags for brick (no waste)
13.51
Bags for block (no waste)
7.69
Total weight
1,920 lb
Total weight in kilograms
871 kg

See the step-by-step solution ↓

Step-by-step solution

  1. Divide the bricks by the bricks one bag lays to see how many bags the brick needs

    50037=13.5135

  2. Divide the blocks by the blocks one bag lays to see how many bags the block needs

    10013=7.6923

  3. Add both together, plus 10% extra for mortar that gets dropped or wasted

    13.5135+7.6923×1+10100=23.3264

  4. Round up to whole bags, since the store sells only full bags

    round up23.3264=24

  5. Multiply the bags by the bag weight to see how much you'll haul

    24×80=1,920 lb

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find out how many bags of mortar mix to buy for your bricks and blocks. Masons usually know how many units a job takes before they think about mortar. It might be so many bricks for a planter, or so many blocks for a foundation course. Premixed mortar is sold by the bag. Makers print how many standard units one bag will lay. So one division turns your brick or block count into a shopping list.

The calculator divides your brick and block counts by the yield per bag (how many units one bag lays). Then it adds a little extra for waste and rounds up to whole bags. The default yields are about 37 standard bricks or 13 standard 8 × 8 × 16 in blocks per 80 lb bag. They come from one maker's published data sheet for its Type N mortar mix. Other products, joint sizes and laying styles lay more or fewer, so check the bag you buy. For a structural or load-bearing wall, the designer and the local building code set the mortar type and strength.

Where it's used

Why this math matters outside the classroom:

  • Garden walls. A homeowner laying 370 bricks at 37 bricks per bag needs exactly 370 ÷ 37 = 10 bags before waste.
  • Block foundations. A crew laying 260 blocks at 13 per bag plans 20 bags, then 22 with 10% extra.
  • Truck loads. Contractors check that 24 bags of 80 lb mortar, 1,920 lb, fits within a pickup's payload rating.
  • Classroom rates. Students treat bricks per bag as a unit rate and divide to find how many bags a given job needs.

Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.RP.A.3.b, 7.RP.A.3. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Enter the number of bricks and the number of 8 × 8 × 16 in blocks. Use 0 for whichever you aren't laying.
  2. Check the bricks and blocks per bag against the yield printed on your mortar bag. Change them if they differ.
  3. Set a waste allowance and the bag weight.
  4. Read the number of bags and the total weight to haul.

What the inputs mean

Bricks to lay
If you only know the wall size, use the brick calculator to count the bricks first. Then enter the count here.
Concrete blocks to lay (8 × 8 × 16 in)
Enter 0 if you are laying only brick.
Bricks laid per bag
Yields assume standard units and typical 3/8 in joints (the mortar lines between units). Some jobs use more mortar: thicker joints, hollow or oversized units, filling cores and parging (a thin coat over the wall face). Lower the figure for those jobs.
Blocks laid per bag
About 13 standard blocks per 80 lb bag. Check your bag.
Extra for waste
Some mortar is always lost to drops, to batches that stiffen before you use them and to uneven joints. Beginners and hot, dry days tend to need more.
Bag weight
Used for the total weight. For a smaller bag, lower the bricks and blocks per bag to match.

Formula and method

bags for brick = bricks ÷ bricks per bag
bags for block = blocks ÷ blocks per bag
bags = round up((bags for brick + bags for block) × (1 + waste ÷ 100))
weight = bags × bag weight

Each brick or block uses a share of a bag, so the brick and block shares add together. Waste is the extra percentage you choose. The total grows by that percentage, then rounds up, because mortar is sold by the whole bag. Rounding allows a tiny margin, so an exact answer like 10 bags isn't pushed to 11 by computer rounding.

The weight is the dry weight you'll carry from the store or have delivered. It helps you check what your vehicle can safely carry (its payload).

Worked example

A garden wall project needs 500 bricks and a foundation course of 100 blocks, with 80 lb bags, typical yields and 10% waste.

  1. Brick: 500 ÷ 37 = 13.5135 bags.
  2. Block: 100 ÷ 13 = 7.6923 bags.
  3. With waste: (13.5135 + 7.6923) × 1.10 = 23.3264 bags.
  4. Round up to 24 bags, which weigh 24 × 80 = 1,920 lb.

Result: Buy 24 bags of 80 lb mortar mix, about 1,920 lb (871 kg) in all.

Understanding the result

The bag count is how many to buy. Running short mid-wall means a second trip. It can also leave a line between batches that dries to a slightly different shade. So a little extra is usually the better risk.

If you mix your own mortar from masonry cement and sand, this count doesn't apply. Work from the volume of mortar instead, as the brick calculator does.

Assumptions and limitations

  • Standard-size bricks and 8 × 8 × 16 in hollow blocks are laid with typical joints, at the yield per bag you enter.
  • The waste allowance covers ordinary losses only.
  • Every bag is the same size and product.
  • Yields vary by product, joint thickness, unit size and the mason's technique. The defaults are typical figures, not a guarantee.
  • Core filling, grouting reinforced cells (filling block holes that hold steel bars), parging and stone veneer use far more material. They aren't covered.
  • The calculator doesn't choose a mortar type or check structural requirements.

Frequently asked questions

How many bricks does an 80 lb bag of mortar lay?

Typical published yields are around 37 standard bricks or 13 standard 8 × 8 × 16 in blocks per 80 lb bag of premixed mortar. Your result depends on joint size and technique. Treat it as a planning number and check the bag.

How much extra mortar should I buy?

An allowance of 5 to 15% is a sensible range to start from. Choose the upper end for a first project, for hot or windy weather, or for a job with many cuts and corners. Those are the times more mortar gets dropped or wasted.

Can I use the same bag count for 60 lb or 40 lb bags?

No. Smaller bags lay fewer units, in proportion to their size. Change the bricks and blocks per bag to the yield printed on the smaller bag. Then set the bag weight, and the count and weight update together.

Which type of mortar should I use?

That depends on the wall, the weather it faces and whether it carries load. Type N is common for above-ground work that doesn't hold up the building. Types S and M are stronger. For anything structural or below ground level, follow the design and local code.

Sources

How this calculator is checked

Method: Unit-rate division by a manufacturer's published yield per 80 lb bag (37 bricks or 13 blocks), plus a percentage waste allowance, rounded up. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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