Concrete Block Calculator
Calculate concrete blocks (cinder blocks / CMUs) for a wall: block count by size, mortar bags, and core-fill grout if you're reinforcing — with waste factor and cost estimate.
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Enter a price per block to estimate cost.
You might also need:Mortar Calculator·Brick Calculator
Block wall math
mortar = blocks ÷ 13 per 80 lb bag · core fill = filled cells × 0.84 cu ft
A 24 × 4 ft wall (96 sq ft) takes 108 standard blocks before waste — order 114 at 5%. Add 9 bags of mortar, and if the wall is reinforced every 32 inches, about 23 cubic feet of grout for the filled cells and bond beam.
Common CMU sizes
| Nominal size | Face area | Per 100 sq ft | Weight |
|---|---|---|---|
| 8×8×16″ standard | 0.89 sq ft | 113 | ~38 lb |
| 4×8×16″ partition | 0.89 sq ft | 113 | ~27 lb |
| 8×8×8″ half | 0.44 sq ft | 225 | ~25 lb |
| 12×8×16″ foundation | 0.89 sq ft | 113 | ~55 lb |
Build notes
- Footing first: block walls need a level concrete footing — size the pour with the concrete calculator.
- Reinforcement: vertical rebar in grouted cells ties the wall to the footing — plan the bar with the rebar calculator.
- Mortar coverage assumes ⅜″ joints; full details and site-mix quantities in the mortar calculator.
- 4–5 ft per day max: let mortar cure overnight before building higher.
Frequently asked questions
How many concrete blocks per square foot?+
A standard 8×8×16 block covers 0.89 sq ft of wall, so you need 1.125 blocks per square foot — call it 113 blocks per 100 sq ft before waste. Half blocks, corner blocks and cuts come out of the same count.
Is there a difference between cinder blocks and concrete blocks?+
Today they are the same product — hollow concrete masonry units (CMUs). "Cinder block" is the old name from when coal cinders were the aggregate. Modern blocks use crushed stone and are stronger; everything on this page applies to both.
How much does a concrete block wall cost?+
Standard 8×8×16 blocks cost $1.50–$3.00 each. With mortar and core fill, DIY materials run $9–$15 per square foot; professionally laid CMU walls run $15–$35 per square foot depending on height, footing and finish.
Do concrete block cores need to be filled?+
Structural and retaining walls typically need cores filled with grout at reinforced cells (often every 24–32 inches, with rebar) or fully for retaining walls. Garden and non-load walls can stay hollow. Filling every core takes about 0.84 cu ft of grout per 8-inch block.
How high can you build a block wall in a day?+
Limit new block work to 4–5 feet of height per day — fresh mortar below cannot carry more weight yet, and the wall can bow or collapse. Let it set overnight before continuing up.