Concrete block calculator
Same idea as bricks, with bigger units.
Your inputs
Your inputs are processed on your device and are not sent to a server.
Example loaded. You can change any value.
There is no figure yet: nothing is calculated until you ask for it.
- Enter your measurements.
- Check the units and the assumptions.
- Press Calculate, or load the example.
Rather see a worked case? Press “Load example” and change any value afterwards.
Next step
The blocks are counted; the joint mortar is the other half of the budget.
Where each number comes from Conversion constants are exact; densities and coverage rates come from cited sources; everything else is an assumption you can change. Methodology · Sources and updates
How to use it
- Measure the wall area.
- Enter the block face size: 16 x 8 in is the most common.
- Adjust the joint, normally 3/8 in.
- Subtract doors and windows if there are any.
How it is calculated
Same principle as brick, but with large units the joint matters much less:
A 16 x 8 in block with a 3/8 in joint occupies 16.375 x 8.375 in = 0.0885 m², giving 11.3 blocks per square metre, or 1.05 per square foot. Without the joint you would get 12.1.
That is also the practical reason to build in block: fewer units, fewer joints, less time.
Worked example
A 215 sq ft wall in 16 x 8 in block, 3/8 in joint, 5 % breakage:
- Module: 16.375 x 8.375 in = 0.0885 m²
- Blocks per m²: 11.3 (1.05 per sq ft)
- With waste: 20 m² x 11.3 x 1.05 = 238 blocks
Good to know
- Weight. A 16 x 8 x 8 in concrete block weighs 30-40 lb. 238 blocks is close to four tons: check access and unloading before ordering.
- Lightweight and aerated blocks. Different sizes and weights, identical maths: measure the face and set the joint.
- Corner blocks. Some systems use special units at corners and reveals. This calculator counts standard units.
Frequently asked questions
How many concrete blocks per square foot?
About 1.05 blocks per square foot with a 16 x 8 in block and a 3/8 in joint, which is 11.3 per square metre. A 20 x 8 in block gives about 0.84 per square foot.
How many blocks for a 215 sq ft wall?
With 16 x 8 in blocks, a 3/8 in joint and 5 % breakage, about 238 blocks. Subtract the area of doors and windows first.
Does this work for aerated or lightweight blocks?
Yes. Enter the real size of the unit you are using. The method is the same: face size plus joint.
Do I need to calculate the mortar too?
If you are building the wall, yes. The mortar calculator uses the same unit and joint sizes and takes the wall thickness into account.