Concrete Block & Fill Calculator
Estimate the number of concrete masonry units (CMU blocks), mortar bags, and grout fill needed for any wall project. Supports block sizes from 4 to 12 inches wide with optional core filling.
Wall Dimensions
Block Configuration
Block Output
Block Size Reference
How to Calculate Block Quantity
Calculating block quantity is based on the face area of each block and the total wall surface.
- Find the Wall Area: Measure the length and height of the wall in feet. Multiply for total square footage: Area = Length × Height.
- Blocks Per Square Foot: A standard 8x8x16 block with ⅜ inch joint covers approximately 1.125 sq ft. Divide 1 by this to get ~0.89 blocks per sq ft.Blocks = Wall Area × Blocks per sq ft × (1 + Waste)
- Mortar Estimation: Plan on one 80lb bag of mortar mix per 35 blocks. Add 10% for waste.
Example Calculation
For a 30 ft long, 8 ft tall wall using 8x8x16 blocks with 5% waste:
- Wall area: 30 ft × 8 ft = 240 sq ft
- Raw blocks: 240 sq ft × 0.89 blocks/sq ft = 214 blocks
- With 5% waste: 214 × 1.05 = 225 blocks
- Mortar needed: 225 ÷ 35 = ~7 bags of 80lb mortar mix
- Grout (full fill): ~7.2 cu ft of grout = 12 bags of 80lb grout mix
Common Block Wall Mistakes
- Not accounting for openings: For walls with doors or windows, subtract the area of each opening from the total wall area before calculating blocks. This calculator uses gross wall area.
- Incorrect mortar mixing: Too much water weakens the mortar. Mix mortar to a peanut butter consistency. Let it slake for 10-15 minutes before use for maximum bond strength.
- Skipping control joints: For walls over 20 feet long, install control joints every 20-25 ft to prevent cracking from thermal expansion and settlement.
Frequently Asked Questions
How many concrete blocks do I need per square foot?
For standard 8x8x16 blocks with a ⅜ inch mortar joint, you need approximately 0.89 blocks per square foot, meaning each block covers about 1.125 sq ft of wall.
How much mortar do I need per block?
One 80lb bag of mortar mix covers approximately 30-40 standard 8x8x16 blocks, including both bed and head joints. Plan for 1 bag per 35 blocks as a safe average.
Should I fill concrete blocks with grout?
Core filling adds structural strength and is required for load-bearing walls, seismic zones, and walls exceeding 8 feet in height. Partial fill (every other core) is common for retaining walls under 4 feet. Non-load-bearing partition walls typically do not require fill.