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Cinder Block Calculator

Find how many cinder, CMU, or cement blocks a wall needs from its length, height, block face size, and total door or window area.

Optional: subtract door/window area from the wall.

Result

180 blocks

A 20 ft x 8 ft wall needs about 180 blocks (16x8in)

Quick Answer

A cinder block calculator subtracts door and window openings from wall area. The tool then divides by the nominal block face area and rounds up. A 20 by 8 foot wall has 160 square feet. With 16 by 8 inch faces and no openings, 160 ÷ 0.8889 gives 180 blocks.

Understanding A Cinder Block Wall Quantity Estimate

A cinder block calculator finds how many full units cover a wall face. It multiplies wall length by height, takes away door and window area, and changes the block face from square inches to square feet. The tool divides net wall area by nominal block face area, rounds up so a part block does not leave the count short, and gives a base count for an early order and plan check on the job site. Block calculator, CMU block calculator, cement block calculator, and block wall calculator searches often use this same area method. The nominal 8 by 16 inch face includes the mortar joint, while bond, corners, cuts, lintels, grout, steel, waste, and wall plans can change the final order.

The Block Wall Formula With Door And Window Deductions

Wall size gives the gross area. Openings reduce that area. Nominal face size covers the wall module, including the planned joint space.

  • Wall area = wall length × wall height.
  • Net wall area = wall area - openings.
  • Block face area in square feet = block width in inches × block height in inches ÷ 144.
  • Blocks = net wall area ÷ block face area, rounded up.

Getting Started With This CMU Block Wall Calculator

Inputs

  • Wall length: the wall length in feet.
  • Wall height: the wall height in feet.
  • Block width: the nominal face length in inches.
  • Block height: the nominal face height in inches.
  • Openings: the total door and window area in square feet.

Steps

  1. Measure wall length and height.
  2. Find the area of each opening.
  3. Add all opening areas.
  4. Check the nominal face size for the chosen block.
  5. Enter all values and read the rounded block count.
  6. Add job waste only after plan review.

Cinder Block Example With Each Step And Rounding Shown

20 ft wall length, 8 ft wall height, 16 in block width, 8 in block height, and 0 sq ft openings.

  1. Wall area: 20 ft × 8 ft = 160 sq ft.
  2. Net area: 160 sq ft - 0 sq ft = 160 sq ft.
  3. Face area in square inches: 16 in × 8 in = 128 sq in.
  4. Face area in square feet: 128 sq in ÷ 144 = 0.888888... sq ft.
  5. Block count: 160 sq ft ÷ 0.888888... sq ft = 180 blocks.

180 blocks. The tool rounds any part-block answer up to the next full block. This example already gives a whole number.

When A Block Wall Material Count Fits Your Project

Use this count for a straight wall with known size, openings, and nominal block face. Ask a mason, designer, engineer, or local office to check bond, lintels, steel, grout, and code needs.

For nearby tools, the construction calculators hub lists every material and quantity calculator, and the glossary defines common calculator terms.

Assumptions

  • The wall face is a rectangle.
  • Openings are entered in square feet.
  • Block face sizes are nominal module sizes.
  • The nominal face includes joint space.
  • The result counts full blocks.

Limitations

  • The result does not count half blocks or special shapes.
  • No waste rate is added.
  • Bond and corners can change cuts.
  • Mortar, grout, steel, and footings need separate plans.
  • Local code and wall plans still apply.

In Practice

A common mistake is entering the real block size, not the nominal module. A nominal 8 by 16 inch face includes the joint space. Check the maker's size data before entry. The result is an estimate and does not replace code, plans, or expert review.

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Frequently Asked Questions About Cinder Block Counts

Are Cinder Blocks And CMU Blocks Counted The Same Way?

The same area method works when both units use the entered nominal face size. Modern wall blocks are often called concrete masonry units, or CMUs, and block strength and weight class do not change the face-area count.

Should Door And Window Openings Be Removed?

Yes, subtract the full door and window area from the gross wall area. Find each opening with width × height, then add them. Lintels, jambs, returns, and cut blocks on the wall still need separate planning.

Does A Standard Block Measure 8 By 16 Inches?

A common block face is 8 inches high and 16 inches long. The real block is smaller so mortar fills the wall grid. Check the maker's size chart when the block or joint size differs.

Does The Count Include Mortar And Reinforcement?

No, the calculator counts full blocks and leaves out other wall materials. Mortar, grout, steel, lintels, ties, footings, odd shapes, and waste need separate takeoffs. Load-bearing walls also need structural plans and building-code review.

Sources

Last updated: . Reviewed for accuracy against the formula shown above.