Concrete Block Calculator

The formula divides your total wall area by the area of a single block's face, then adds your waste buffer. A standard nominal 16 by 8 inch block covers about 0.89 square feet of wall, including its mortar joint, so dividing your wall's square footage by that figure gives a quick raw estimate before waste.

Nearly every standard concrete block sold in the US shares that same 16 by 8 inch face, no matter how thick it is. The block's width, sometimes called its nominal size, only changes the wall's overall thickness, weight, and volume, not the block count, since the count is based purely on the face you actually see and mortar between.

Enter the combined area of any doors, windows, or other openings in the Openings field and the calculator subtracts them for you automatically, so you don't need to work out net wall area by hand first. As a reference, a standard door is roughly 21 square feet (3 by 7 feet), a standard window is roughly 16 square feet (4 by 4 feet), and a single-car garage door is roughly 168 square feet (8 by 7 feet).

How Much Mortar Will I Need?

Mortar estimates vary a lot depending on joint thickness and mortar type, anywhere from about 3 to 7 bags per 100 blocks across different published guidance, so this calculator deliberately does not bundle a single mortar figure into the block count above. Use our Mortar Calculator separately, where you can set your own blocks-per-bag coverage rather than relying on an assumption that may not match your actual mortar mix.

Enter a price per block if you know roughly what your supplier charges, and the calculator multiplies it by the block count above to estimate your material cost. Leaving this field at 0 skips the cost estimate entirely; it does not assume any particular price on your behalf, since block prices vary significantly by region, block type, and supplier.

This cost estimate covers blocks only. It does not include mortar, sand, delivery, or labor, all of which add meaningfully to a real project budget.

Most concrete blocks sold today are hollow, with two or three open cores running through the center, and this is what most people mean when they say cinder block, even though true cinder blocks (made with coal cinder aggregate) are largely a thing of the past. Modern units are properly called concrete masonry units, or CMU, made with a denser aggregate.

The block count formula above works identically whether your blocks are hollow or solid, since it's based on the face area you see on the wall, not what's happening inside the block. Hollow and solid blocks of the same face size cover the same wall area; solid blocks are simply heavier and typically cost more per unit.

If you're filling the hollow cores of your wall with grout or concrete, for reinforcement or added strength, that's a separate calculation from the block count here. Our Concrete Block Fill Calculator works out the fill volume based on your block size and how many cores you're filling.

This formula works the same for a below-grade foundation wall as it does for any above-grade CMU wall, since block count depends only on wall area and block face size, not on what's on either side of the wall. Enter your foundation wall's length and height the same way.

A true retaining wall is usually a different product entirely. Most retaining walls use segmental retaining wall units, purpose-made interlocking blocks with a built-in batter (a slight backward lean) and a lip or pin system that locks each course to the one below, not standard CMU. If you're planning a retaining wall specifically, use our Retaining Wall Calculator instead, which accounts for that interlocking geometry and backfill.

These related tools cover the other materials and wall types a block project usually needs:

• Concrete Volume Calculator - for a poured concrete footing or slab
• Brick Calculator - for a clay brick wall instead of concrete block