# How many bags of mortar do I need?

Estimates the bricks or blocks in a wall, the mortar volume for their joints, and the 80 lb bags of mortar mix to buy, from the wall size, unit size, joint thickness and waste.

- Page: https://www.acalculator.org/construction/mortar-calculator
- JSON spec: https://www.acalculator.org/construction/mortar-calculator.json
- Version: 9d074f3d26be

## Default answer

Example with the default inputs (Wall length (ft) 20, Wall height (ft) 4, Laying Bricks, Joint thickness (in) 0.375, Waste allowance 10%): For 549 bricks, buy about 18 80 lb bags of mortar mix.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| l | Wall length (ft) | The length of the wall face, in feet. |
| h | Wall height (ft) | The height of the wall face, in feet. |
| unit | Laying | Standard modular bricks or standard 8 in concrete blocks. |
| ul | Unit length (in, optional) | The actual length of one brick or block; empty uses 7 5/8 in (brick) or 15 5/8 in (block). |
| uh | Unit height (in, optional) | The actual height of one unit; empty uses 2 1/4 in (brick) or 7 5/8 in (block). |
| ud | Unit depth (in, optional) | The wall thickness, the depth of one unit; empty uses 3 5/8 in (brick) or 7 5/8 in (block). |
| j | Joint thickness (in) | The mortar joint; 3/8 in (0.375) is standard. |
| pb | Units per 80 lb bag (optional) | How many units one bag lays; empty uses the Sakrete figure: 35 bricks or 12 blocks. |
| w | Waste allowance | Extra mortar for spills, droppings and mixing leftovers. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| bags | 80 lb bags of mortar mix | ⌈units × (1 + waste) ÷ units per bag⌉. |
| units | Bricks or blocks | ⌈wall area ÷ ((unit length + joint) × (unit height + joint))⌉. |
| volume | Mortar volume (ft³) | The joints’ volume with the waste allowance, in cubic feet. |
| yards | Mortar volume (yd³) | The same volume in cubic yards (27 ft³ = 1 yd³). |
| perUnit | Mortar per unit (in³) | ((length + joint)(height + joint) − length × height) × depth. |
| area | Wall area (ft²) | Wall length × wall height. |
| name | Units | Bricks or blocks. |

## Method

Units = ⌈144 × wall area (ft²) ÷ ((l + j)(h + j))⌉; mortar = units × ((l + j)(h + j) − l h) × d × (1 + waste) ÷ 1,728 ft³; bags = ⌈units × (1 + waste) ÷ units per bag⌉.

## Assumptions

- A single-wythe wall, each unit with one bed joint and one head joint; cores of hollow blocks are not filled.
- Standard sizes: modular brick 7 5/8 × 2 1/4 × 3 5/8 in, concrete block 15 5/8 × 7 5/8 × 7 5/8 in, with 3/8 in joints.
- Bags use the maker’s yield (Sakrete Type S and Type N: 35 bricks or 12 blocks per 80 lb bag); yields vary with the joint and the mason.
- The waste allowance is yours to set; the default 10% is not from a maker.

## Worked examples

1. l = 20, h = 4, unit = brick, j = 0.375, w = 10% gives units = 549, bags = 18, perUnit = 13.933594, volume = 4.869501, area = 80. Source: Sakrete, Mortar Mix Type S (an 80 lb bag lays 12 standard 8 in blocks or 35 standard bricks), https://www.sakrete.com/product/mortar-mix-type-s/ (retrieved 2026-10-02).
2. l = 32, h = 6, unit = block, j = 0.375, w = 0% gives units = 216, bags = 18, perUnit = 67.552734, volume = 8.444092, yards = 0.312744. Source: Sakrete, Mortar Mix Type N (an 80 lb bag lays 12 standard 8 in blocks or 35 standard bricks), https://www.sakrete.com/product/mortar-mix-type-n/ (retrieved 2026-10-02).
3. l = 10, h = 3, unit = brick, j = 0.5, pb = 37, w = 5% gives units = 194, bags = 6, perUnit = 18.804688. Source: Sakrete, Mortar Mix Type S (an 80 lb bag lays 12 standard 8 in blocks or 35 standard bricks), https://www.sakrete.com/product/mortar-mix-type-s/ (retrieved 2026-10-02).

## FAQ

### How many bags of mortar do I need for bricks?

Sakrete says an 80 lb bag of its Type S or Type N mortar mix lays 35 standard bricks. Divide your brick count by 35 and round up, after adding a waste allowance. A 20 × 4 ft wall takes 549 bricks, so 549 × 1.1 ÷ 35 = 17.3, or 18 bags.

### How many blocks does an 80 lb bag of mortar lay?

Sakrete gives 12 standard 8 in blocks per 80 lb bag for its Type S and Type N mortar mixes. A 32 × 6 ft block wall has 216 blocks, so 18 bags before any waste.

### How do I calculate the number of bricks in a wall?

Divide the wall area by the face of one brick plus one joint. A modular brick is 7 5/8 × 2 1/4 in; with 3/8 in joints that is 8 × 2 5/8 = 21 in², so a square foot (144 in²) holds 144 ÷ 21 = 6.86 bricks.

### How is the mortar volume worked out?

Each unit gets one bed joint and one head joint. The mortar per unit is ((length + joint) × (height + joint) − length × height) × depth. For a modular brick with 3/8 in joints: (21 − 17.156) × 3.625 = 13.93 in³.

### How much waste should I allow?

The page uses 10% unless you change it; the makers’ pages give no waste figure. Mortar is lost to droppings, spills and batches that set before use, so beginners often allow more.

### Should I use Type S or Type N mortar?

Sakrete titles its Type S mix for laying wall blocks and its Type N mix for brick laying and joint repair. Follow your plans or local code; on Sakrete’s pages both lay the same number of units per bag.

## Sources

- Sakrete, Mortar Mix Type S (product page: an 80 lb bag lays 12 standard 8 in blocks or 35 standard bricks, or sets 10 ft² of cultured stone). https://www.sakrete.com/product/mortar-mix-type-s/ (retrieved 2026-10-02)
- Sakrete, Mortar Mix Type N (product page: an 80 lb bag lays 12 standard 8 in blocks or 35 standard bricks). https://www.sakrete.com/product/mortar-mix-type-n/ (retrieved 2026-10-02)