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Concrete, Masonry & Stone

Mortar Calculator

Work out mortar bags and masonry sand for a block or brick wall from the unit count and joint size.

Your measurements

What you are laying
If you do not have a count yet, run the block or brick calculator first.
Mix
Type S is the usual choice anywhere the wall meets soil or takes lateral load.

Your result

Sample values

17

Bags of mortar

450

Block laid

0.9

Tons of sand

25.5

Cubic feet of mortar

Type N, ⅜ in joints, 10% waste. 80 lb bags.

What to order

Item Quantity
Mortar mix, 80 lb bags 17 bags
Masonry sand 0.9 tons
Pallets of sand, if bagged 18 bags
Water, approximate 85 gallons

How to use this calculator

Enter how many units you are laying and the joint thickness you are working to. If you have not counted the units yet, the block or brick calculator will give you that figure first.

Pick the mortar type for where the wall sits rather than for strength alone. Type N is the default above grade, Type S is the usual choice below grade or where the wall takes sideways load, and Type M is for foundations and retaining structures.

Formula

Mortar volume = Units × Mortar per unit

Bags = Mortar volume ÷ Yield per bag

Sand = Bags × Sand per bag

Mortar per unit
depends on unit size and joint thickness
Yield per bag
about 1.5 ft³ of mortar from an 80 lb bag with sand

Pre-mixed bags already contain sand; mix-only products need sand ordered separately.

Worked example

450 standard 8 in block, ⅜ in joints, Type N, 80 lb bags, 10% waste.

  1. 450 block × 0.0515 ft³ of mortar each = 23.2 ft³
  2. 23.2 ft³ × 1.10 = 25.5 ft³ with waste
  3. 25.5 ft³ ÷ 1.5 ft³ per bag = 17 bags
  4. 17 bags × 0.106 tons of sand each = 0.9 tons

17 bags of Type N and about 0.9 tons of sand

Understanding your results

Mortar quantities move around more than most materials on a job. Joint thickness is the biggest lever — going from ⅜ in to ½ in raises the mortar volume by roughly a third for the same wall. How much falls off the board and how much sits in the mixer at the end of the day are real losses that the waste allowance is there to cover.

Check whether your product is a complete mix or a mortar cement that still needs sand. Bagged pre-mix is simpler for small jobs and much more expensive by volume; buying cement and sand separately pays off somewhere around a pallet.

Questions

About this calculator

Ask something else

Around 27 standard 8 in block per 80 lb bag of pre-mixed mortar with ⅜ in joints, or roughly 125 modular bricks. Both figures drop noticeably with thicker joints or a cold, stiff mix that gets discarded rather than retempered.

Mortar has more cement and finer sand, no coarse aggregate, and is designed to stay workable and bond to units. Concrete has stone in it and is designed for compressive strength. Concrete makes poor mortar and mortar makes weak concrete — they are not interchangeable.

No. Mortar can be retempered with a little water within its working life, usually a couple of hours, but once it has begun to set it should be discarded. Mortar that has stiffened and been re-wetted repeatedly will not reach its rated strength.

Roughly five quarts for an 80 lb bag, but go by consistency rather than volume. Mortar is right when it holds a ridge on the trowel without slumping and does not run off a vertical face. Sand moisture varies enough that a fixed water figure is only a starting point.

Keep going

All Concrete, Masonry & Stone tools
Estimates, not specifications. Results are based on the values you enter and on typical material properties. Densities, coverage rates and product sizes vary between suppliers, so confirm quantities against your supplier's data before ordering. Structural work must be signed off by a qualified professional and meet your local building code.