Brick and block calculator for a wall, with the mortar

How to calculate bricks per square foot

Divide 144 by (length + joint) × (height + joint), all in inches. A modular brick of 7 5/8 × 2 1/4 in with 3/8 in joints takes up 8 × 2 5/8 = 21 square inches of wall face, so one square foot needs 144 ÷ 21 = 6.86 bricks. The Brick Industry Association (BIA) tables say 6.75, because they count three modular courses as exactly 8 in. The brick's depth does not change the count: it sets the thickness of the wall.

The calculator adds up your walls, takes off doors and windows and multiplies the net area by the units per square foot. Then it adds 5% for breakage and cuts, the minimum the BIA advises on top of the net count, and rounds up. For 8 × 8 × 16 concrete blocks the Concrete Masonry & Hardscapes Association (CMHA, formerly NCMA) gets 119 blocks per 100 sq ft with the same 5%, and so does the calculator.

Mortar is counted in pounds of mortar mix per square foot of wall. The CMHA TEK 04-02A says one 80 lb bag of preblended mortar lays about 50 brick-sized units or 16 standard blocks. That is 1.6 lb per brick × 6.75 bricks = 10.8 lb per sq ft, and 5 lb per block × 1.125 blocks = 5.6 lb per sq ft. For utility bricks the calculator scales the brick figure by the BIA mortar volumes (3.7 cu ft per 100 sq ft against 5.5 for modular): 7.3 lb per sq ft. The total divided by the bag weight gives the bags. Sizes, joint, extra and mortar rate are all in the advanced options.

A worked example

In feet and inches (US). The calculator opens with a 20 × 8 ft wall of modular brick, 3/8 in joints and one 3 × 4 ft window.

• Wall: 20 × 8 = 160 sq ft; window 3 × 4 = 12 sq ft; net area 148 sq ft
• Bricks: 148 × 6.86 = 1,014.9; with 5% extra 1,065.6, so 1,066 bricks
• Mortar: 148 × 10.8 = 1,598 lb; in 80 lb bags 19.98, so 20 bags (or 27 bags of 60 lb)

The same wall in utility brick takes 467 bricks and 14 bags; in 8 × 8 × 16 CMU, 175 blocks and 11 bags.

In metres (UK and elsewhere). A 5 × 2.7 m wall with a 1.2 × 1.4 m window is 11.82 m² net. UK bricks of 215 × 65 mm with 10 mm joints come to 59.26 per m², so 736 bricks with 5% extra. At 60 kg of dry mortar per m² (the CVR data sheet figure for a 12 cm solid brick wall) that is 709 kg, or 29 bags of 25 kg.

Bricks and blocks per 100 square feet

Units for 100 sq ft of net wall with 3/8 in joints and 5% extra, and 80 lb bags of mortar mix at the CMHA rates. The figures come from the calculator.

Unit	Actual size	Per sq ft	Per 100 sq ft with 5%	80 lb bags per 100 sq ft
Modular brick	7 5/8 × 2 1/4 in	6.86	720	14
Utility brick	11 5/8 × 3 5/8 in	3	315	10
Concrete block (CMU) 8 × 8 × 16	15 5/8 × 7 5/8 in	1.125	119	7

In metres with 10 mm joints and 5% extra: a UK brick of 215 × 65 mm gives 59.26 per m², or 623 for 10 m²; a UK block of 440 × 215 mm gives 9.88 per m², or 104 for 10 m².

Buying bricks, blocks and mortar mix

Concrete blocks are named by their nominal size, 8 × 8 × 16, but each side is 3/8 in shorter so that block and joint add up to the round figure: a standard block measures 7 5/8 × 7 5/8 × 15 5/8 in. Enter the actual size in the calculator, not the name. UK blocks are usually 440 × 215 × 100 mm and UK bricks 215 × 102.5 × 65 mm.

QUIKRETE sells its Mortar Mix, a Type N mortar that needs only water, in 10, 40, 60 and 80 lb bags; the calculator starts with 80 lb. Its own chart is more cautious than the CMHA: up to 37 bricks or 13 blocks per 80 lb bag. If you would rather follow the bag, set the mortar rate to 14.6 lb per sq ft for modular brick (80 ÷ 37 × 6.75) or 6.9 lb for CMU (80 ÷ 13 × 1.125).

The UK and European figures are for 25 kg bags of dry ready-mixed mortar. The 50 kg/m² rate for concrete blocks comes from a data sheet for 200 mm blocks, so it is generous for 100 mm blocks: lower it if your supplier gives a figure.

Common mistakes

• Adding the joint to the nominal size. An 8 × 16 block counted as 8 3/8 × 16 3/8 in gives 1.05 blocks per sq ft instead of 1.125, about 7% short.
• Leaving the joint out. A modular brick with no joint gives 8.39 per sq ft instead of 6.86, 22% more than you need.
• Counting a double-wythe wall once. A wall two bricks thick has two layers: add it as a second wall with the same size.
• No extra for cuts. Bricks get cut around doors and windows and broken ones are lost: 5% is the minimum.
• Buying portland cement instead of mortar mix. A bag of cement is only the binder; mortar also needs sand and usually lime. Mortar mix already contains them.