Free material estimator

Concrete Block Calculator

Use this concrete block calculator to estimate blocks to buy for ordinary rectangular CMU, cinder, and hollow block walls. Add walls, subtract openings, and adjust waste.

No signup

Multiple walls

Opening deductions

Calculate your concrete blocks

Start with the wall length and height. The live result separates base blocks from the editable project waste allowance.

Blocks to Buy

198

180 base + 18 waste

Unit:

Wall 1

Length (ft)

Height (ft)

Openings (0)

Openings (Doors & Windows)

Block, waste, and price settings

8×8×16 Standard · 0 openings · 10% waste

Nominal Block Size

Nominal Block Preset

Use custom nominal module

Presets and custom values use nominal module dimensions. Do not add the mortar joint again.

Waste Allowance10%

10% is an editable planning allowance. Adjust it for your layout, cuts, and breakage.

Cost Estimation

Enable to enter local prices and see estimated cost.

Concrete Block Material Estimate
Assumptions: Imperial (ft); 8×8×16 Standard nominal 16 x 8 in face module; 10% project waste
Wall 1: 20 x 8 ft; 160 gross, 0 openings, 160 net, 180 base blocks, 0 blocks saved
Project: 160 gross, 0 openings, 160 net
180 base blocks + 18 waste = 198 blocks to buy
Mortar: 22 60-lb bags
Estimate only. Blocks and mortar materials only. Labor and installed cost are excluded.

How the concrete block calculator estimates your order

The estimate follows one checkable path. Openings are subtracted before the net wall area is divided by the nominal block face module. Waste is added once to the combined project base count.

Ordinary foundation walls and garage walls use the same wall-block math when you enter length and height. Footings, reinforcement, and structural design stay outside the block count.

WALL DIMENSIONS AND OPENINGS

length x height minus door and window openings = net wall area

NOMINAL FACE MODULE

8 x 16 · 1.125 blocks / sq ft

BASE BLOCKS

180

10% WASTE

+18

BLOCKS TO BUY

198

The calculator subtracts openings first, converts net wall area into nominal block modules, then adds the selected project waste allowance.

Worked example: 20 x 8 ft wall

120 ft x 8 ft = 160 sq ft net wall area
2160 sq ft x 1.125 blocks per sq ft = 180 base blocks
3180 x 10% = 18 waste blocks
4180 + 18 = 198 blocks to buy

The default 10% is an editable planning allowance for cuts and breakage, not a universal requirement.

Choose the right masonry task

This page counts standard wall blocks. Use a dedicated calculator when the material or construction method changes.

Joint mortar

Estimate whole 80-lb or 60-lb mortar bags with editable product coverage and an order buffer.

Open mortar calculator

Core fill or grout

Estimate grout volume for selected CMU cells instead of treating fill as wall block count.

Open fill calculator

Retaining wall materials

Count landscape blocks, caps, base gravel, and drainage backfill with retaining-wall formulas.

Open retaining wall calculator

Installed wall cost

Estimate blocks, mortar, optional grout, labor, and editable regional planning costs.

Open wall cost calculator

Block weight, pallet loading, transport, and curved or irregular walls are not calculated here. No empty estimate is provided for those tasks.

Nominal CMU size and wall coverage

Block presets use nominal module dimensions. A nominal 8 x 8 x 16 in CMU uses a 16 x 8 in wall-face module, which covers 0.889 sq ft or 1.125 blocks per sq ft. The matching Metric face module is 400 x 200 mm, or 12.5 blocks per square meter. Do not add the mortar joint a second time.

Specified CMU dimensions are typically 3/8 in smaller than nominal dimensions. That difference leaves room for the mortar joint so the installed unit fits the nominal layout module.

Nominal size	Metric module	Blocks / sq ft	Blocks / m2	Planning use
4 x 8 x 16 in	100 x 200 x 400 mm	1.125	12.5	Partitions and veneer layouts
6 x 8 x 16 in	150 x 200 x 400 mm	1.125	12.5	Thinner CMU wall layouts
8 x 8 x 16 in	200 x 200 x 400 mm	1.125	12.5	Common CMU wall module
10 x 8 x 16 in	250 x 200 x 400 mm	1.125	12.5	Wider CMU wall layouts
12 x 8 x 16 in	300 x 200 x 400 mm	1.125	12.5	Wider CMU wall layouts

Sources and estimate scope

Last reviewed July 2026

Technical references support the block module and mortar planning assumptions. Confirm local unit dimensions, packaging, and product yield with your supplier before ordering.

CMHA CMU-TEC-001

Dimensional basis for typical nominal CMU modules and specified dimensions that are commonly 3/8 in smaller.

QUIKRETE Mortar Mix data sheet

Lists up to 13 standard 8 x 8 x 16 blocks per 80-lb bag. The dedicated mortar calculator uses a conservative purchase allowance.

Material estimate, not structural approval

This calculator estimates blocks and an auxiliary mortar quantity for ordinary rectangular CMU walls, including foundation and garage wall layouts entered by length and height. It does not design rebar, bond beams, lintels, footings, or reinforcement. It does not check building code, permits, structural capacity, or engineering approval, and it is not a contractor bid.

Frequently asked questions

How many concrete blocks do I need per square foot?

A nominal 8 x 8 x 16 in CMU uses a 16 x 8 in face module. It covers about 0.889 square feet, so the estimate uses 1.125 blocks per square foot before waste. The same nominal face in Metric is 400 x 200 mm, or 12.5 blocks per square meter.

Why does a 20 x 8 ft wall need 180 base blocks?

The wall has 160 square feet of net area. Multiplying 160 by 1.125 blocks per square foot gives 180 base blocks. A 10% planning allowance adds 18, for 198 blocks to buy.

Does nominal 8 x 8 x 16 include the mortar joint?

Yes. Nominal size is the installed layout module. The specified CMU is typically 3/8 inch smaller in each modular direction so the unit and mortar joint fit the nominal module. Do not add the joint again.

Should I always add 10% waste?

No. Ten percent is the editable starting allowance in this calculator, not a universal rule. Adjust it for cuts, breakage, layout complexity, supplier packaging, and your own project conditions.

Can I subtract doors and windows?

Yes. Add each opening to its wall. The calculator shows gross area, opening area, net area, blocks saved, base blocks, and the final purchase quantity.

Can I use this for cinder, hollow, or CMU block walls?

Yes, when those terms refer to ordinary rectangular concrete masonry units, including standard hollow CMU. Choose the correct nominal block module and confirm the actual product with your supplier. AAC, glass block, curved walls, and specialty masonry systems stay outside this calculator.

Does this calculator cover retaining walls or structural design?

No. Use the retaining wall calculator for landscape blocks, caps, gravel, and backfill. Rebar, lintels, code, permits, and structural approval require project documents and qualified local professionals.

Is the cost result a contractor bid?

No. Optional homepage pricing covers blocks and mortar materials only. It excludes labor, footings, permits, reinforcement, waterproofing, delivery, and other installed-cost items.