What are standard CMU dimensions?

Standard concrete masonry units (CMU) are identified by nominal dimensions that include a standard 3/8-inch mortar joint. For example, a nominal 8" x 8" x 16" block has actual manufactured dimensions of 7-5/8" high x 7-5/8" deep x 15-5/8" long.

How many standard 8x8x16 blocks are in a square foot?

With standard 3/8-inch joints, an 8" x 16" nominal face covers 128 square inches (0.8889 sq ft). This yields approximately 1.125 blocks per square foot of wall face area.

How many blocks does one bag of mortar lay?

Mortar yield depends heavily on bag weight, block wall thickness (4", 6", 8", or 12"), joint width, and waste. For example, QUIKRETE cites up to 13 standard 8x8x16 blocks per 80-lb bag of Mortar Mix (#1102). Always verify coverage against the specific mortar manufacturer data sheet.

What waste allowance should I plan for?

A 5% to 10% waste allowance is common for straight uninterrupted runs. Increase waste to 10% to 15% for walls with multiple openings, corners, or angle cuts.

Can this calculator be used for structural retaining walls?

This calculator estimates face unit takeoffs and bed/head joint mortar bags only. Structural retaining walls require site-specific engineering for soil lateral loads, reinforced concrete footings, rebar schedule, drainage, and grout fill.

Block Calculator

Estimate concrete masonry units (CMU), mortar bags, and material costs with custom joints, waste, and manufacturer bag yields.

Wall & Material Inputs

Wall Length (ft)

Wall Height (ft)

Block Size (nominal width × height × length)

Mortar Joint Thickness (in)

Openings Deduction (doors, windows) area (sq ft)

Waste Factor (%)

Mortar Bag Coverage (blocks per bag)

Default 13 blocks/bag represents rated yield for QUIKRETE 80-lb Mortar Mix (#1102) with 8x8x16 CMU. Adjust per your bag size and data sheet.

Cost Estimation (Optional)

Currency:

Cost per Block

Cost per Mortar Bag

Results & Estimates

Enter dimensions and click Calculate

Summary

Estimate concrete masonry units (CMU), mortar bags, and material costs with custom joints, waste, and manufacturer bag yields.

How it works

Enter the wall length and height in feet or meters.
Select the nominal CMU block size (4", 6", 8", or 12" wide units).
Adjust the mortar joint thickness (standard modular joint is 3/8 in / 9.5 mm).
Subtract any door, window, or beam openings.
Set a waste factor for cuts and breakage, plus your mortar bag rated coverage.
Optionally enter unit prices for blocks and mortar to estimate total material expense.

Use cases

Estimating CMU block quantities for straight partition, foundation, or stem walls.
Determining required 6-inch or 8-inch CMU blocks for residential or commercial walls.
Calculating manufacturer-specific mortar bag quantities from technical data sheets.
Budgeting masonry unit and mortar costs before purchasing materials.
Accounting for window and door openings to avoid excessive over-ordering.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu