Block Mortar Calculator

Mortar is the binding material between concrete blocks, and getting the quantity right prevents costly shortages or over-ordering on masonry projects. Enter your number of blocks and select your block size, mortar type, joint thickness, and waste factor into the Block Mortar Calculator to get the mortar you'll need. Results include 60 lb and 80 lb pre-mixed bag counts, total mortar volume in cubic feet, and individual raw material quantities — Portland cement, hydrated lime, and sand — if you're mixing from scratch.

Enter the total number of concrete blocks for your project

Select the appropriate mortar type for your application

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Add percentage for waste and spillage (typically 10-15%)

Results

60 lb Pre-Mixed Bags

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80 lb Pre-Mixed Bags

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Total Mortar Volume

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Portland Cement

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Hydrated Lime

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Sand

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Frequently Asked Questions

How much mortar do I need for 100 concrete blocks?

For 100 standard 8"×8"×16" blocks with 3/8" joints, you'll typically need about 12-15 bags of 60 lb pre-mixed mortar, depending on the mortar type and waste factor.

What's the difference between mortar types O, N, S, and M?

Type O is for interior/low-load applications, Type N is general purpose for most projects, Type S is for below-grade and high-strength needs, and Type M is for high-load structural applications.

Should I use 60 lb or 80 lb mortar bags?

Both will work for your project. 60 lb bags are easier to handle and mix, while 80 lb bags require fewer bags overall but are heavier to work with. Choose based on your physical capabilities and preference.

How do I calculate mortar for different block sizes?

Larger blocks require more mortar per unit due to increased bed joint area and potentially thicker head joints. This calculator accounts for different standard block sizes automatically.

What waste factor should I use for mortar?

A 10-15% waste factor is typical for mortar projects to account for spillage, mixing waste, and application loss. Use 10% for experienced masons and 15% for DIY projects.

Can I mix my own mortar instead of using pre-mixed bags?

Yes, you can mix mortar from raw materials (cement, lime, sand). This calculator provides the quantities needed for both pre-mixed bags and individual components for on-site mixing.

How thick should mortar joints be for concrete blocks?

Standard mortar joint thickness for concrete blocks is typically 3/8 inch, though 1/4 inch and 1/2 inch joints are also used depending on the application and aesthetic preferences.

How do I estimate mortar by wall area instead of block count?

You can estimate by calculating the number of blocks first: divide wall area by the face area of one block, then use this calculator. Standard 8"×16" face blocks cover approximately 0.89 square feet each.