How many concrete blocks per square foot?

1.125 standard blocks (8x8x16) per square foot of wall area including mortar joints. A 100 sq ft wall needs about 113 blocks before waste.

How much mortar for concrete blocks?

One 80lb bag of mortar mix lays about 33 standard blocks. A 200-block wall needs roughly 6 to 7 bags of type S or type N mortar.

Do I need rebar in a block wall?

Yes for structural, load-bearing, and retaining walls. Code requires vertical rebar every 4 ft and horizontal rebar (bond beam) every 4 ft of wall height.

How much does a concrete block cost?

$1.50 to $2.50 per standard 8x8x16 block. A 100 sq ft wall costs $170 to $280 in blocks alone, plus $50 to $80 in mortar.

What is the difference between concrete block and cinder block?

Modern blocks are all concrete (CMU). True cinder blocks used coal ash aggregate and are no longer manufactured. The terms are used interchangeably today.

What type of mortar for concrete blocks?

Type S for below-grade, structural, and load-bearing walls. Type N for above-grade, non-structural walls and veneer. Type S is stronger (1,800 PSI vs 750 PSI).

How do I cap a block wall?

Use solid cap blocks or pour a concrete bond beam on top. Cap blocks are 2x8x16 inches and sit flat on the top course. Always cap before adding a ledger or plate.

Can I build a block wall without mortar?

Dry-stacked block walls use surface bonding cement instead of mortar. They are faster to build but limited to non-structural garden walls and short retaining walls.

BuildingCinder Block Calculator

Cinder Block Calculator

Estimate cinder blocks, CMU mortar, openings, waste, and core-fill grout.

Wall Dimensions

Common walls

Length (ft)

Height (ft)

Block Size

Ready to calculate

Enter wall dimensions or choose a preset.

Last updated June 2, 2026 by our expert review team

CMU Planning Reference

Planning item	Use	Why it matters
Net wall area	Subtract openings	Avoid ordering blocks for doors and windows.
Nominal face module	8 x 16 in	The module includes the typical mortar joint.
Waste allowance	5% to 15%	Covers cuts, corners, and breakage.
Filled-cell share	From your drawings	Do not guess reinforcement or grout layout.

Expert Contributors

Creator

Ehsan Ghazanfari

Licensed Structural Engineer

Ehsan Ghazanfari

Licensed Structural Engineer

FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.

See full profile

Expert Review

Hawkin

Certified Cost & Estimating Professional

Hawkin

Certified Cost & Estimating Professional

AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.

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Updated June 2026

How we verify our calculators

CMU Wall Planning Guide

Start with the nominal block module, subtract openings, then plan filled cells from the structural drawings.

Concrete masonry wall planning guide showing a nominal CMU module with a three-eighth inch mortar joint, a window opening to subtract, and selected grouted cells with a reminder to verify rebar layout locally.

The block count is a material takeoff. Reinforcement, bond beams, grout locations, and footing details still belong in the project design.

Pro Tips

Subtract windows and doors before ordering. Then add a modest waste allowance for cuts, corners, and breakage.

Standard CMU planning uses the nominal module. An 8 x 16 inch face includes the mortar joint in the layout.

Use the filled-cell percentage only when you have a reinforcement or grout plan. Structural walls need local design review.

For the footing below the wall, use the concrete footing calculator.

For a reinforcement takeoff from drawings, use the concrete rebar calculator.

How the Calculator Works

The calculator finds the gross wall area, subtracts openings, and applies the nominal 8 x 16 inch CMU face module. The selected width changes wall thickness and price, but not the face count.

Net area

length x height - openings

Blocks

net area x 1.125 x waste

Mortar

blocks / 13 bags

Quick Reference

Standard face: 8 x 16 in
Blocks per sq ft: 1.125
80 lb mortar bag: about 13 blocks
Typical joint: 3/8 in
Openings: subtract first

Core-Fill Grout for Cinder Block Walls

The calculator can estimate filled-cell volume, but the fill pattern should come from the wall design. Bond beams, pilasters, lintels, and reinforced cells are not optional guesswork.

Partial fill

Only marked cells

Common around rebar, corners, and openings.

Bond beam

Horizontal course

Often used near the top of walls or at load points.

Fully grouted

Every cell

Heavy structural takeoff. Verify mix, lift height, and inspection rules.

Concrete Block Estimates for Common Projects

Garden wall

12 x 3 ft, 10% waste

45 blocks | 4 mortar bags

Short wall with no opening deduction.

Partition wall

20 x 8 ft, 10% waste

198 blocks | 16 mortar bags

Interior takeoff before door deductions.

Foundation section

40 x 4 ft, 15% waste

207 blocks | 16 mortar bags

Use drawings for filled cells and reinforcement.

Metric utility wall

6 x 2.4 m, 2 m2 opening

166 blocks | 13 mortar bags

Metric example with one opening deducted.

Concrete Block FAQ

How many concrete blocks are in a square foot?

A standard 8 x 16 inch nominal block face works out to about 1.125 blocks per square foot.

Should I subtract windows and doors?

Yes. Subtract opening area before adding waste so the order reflects the wall you will actually build.

How much mortar do I need?

QUIKRETE estimates about 13 standard blocks per 80 lb Mason Mix bag. Site conditions and joint tooling can change the yield.

Does block width change the block count?

Not when the face stays 8 x 16 inches. Width changes wall thickness, handling, and price.

How much waste should I add?

Start near 10 percent for a simple wall. Increase the allowance when the layout has more cuts, corners, or breakage risk.

How much grout fill do I need?

Use the filled-cell percentage only as a takeoff helper. Get the required cell layout and grout volume from the structural details and block producer data.

Is this a retaining wall calculator?

No. Use the retaining wall calculator for landscape wall quantities and consult a professional for structural walls.

Do CMU walls need a footing?

Many walls do. Footing width, depth, reinforcement, and frost protection depend on the wall and local requirements.

CMU Planning Mistakes

Counting gross area only

Subtract openings before ordering blocks, then add waste for cuts and breakage.

Treating actual size as the module

Use nominal dimensions for layout. The module includes the mortar joint.

Guessing filled cells

Use the structural drawings. Grout and rebar layouts depend on the wall design.

Using mortar bags as an exact promise

Bag coverage is a planning estimate. Joint thickness, tooling, and waste change field yield.

Important Disclaimer

These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.