Concrete blocks are an inexpensive and versatile building material ideal for the construction of utility buildings like garages. Most concrete blocks are a combination of cement and an aggregate of coal ash (which is why they are also called cinder blocks). Most concrete blocks have holes called cores. These serve to make concrete blocks lighter and less expensive. For a doityourself project, it also means they are a lot easier to handle.
Things You'll Need
 Blueprints
 Tape measure
 Calculator

Determine the height and length of each wall of the proposed garage. If you are working from a set of blueprints, you'll find the figures there. Otherwise, use a tape measure to find the length of each wall, using the foundation as a guide after it has been laid. Since the building doesn't exist yet, you will have to decide on or estimate the height. To be on the safe side, you should allow about 10 feet.

Calculate the number of square feet in the walls. Multiply the length times the height of each wall. Then add up the results. For example, for a 15by30foot garage with walls 10 feet high, you have two walls that are 15by10 feet and that are 30by10 feet. This gives you a total of 900 square feet.

Figure the area of the garage door by multiplying the planned width by the height. For example, if the door will be 10 feet wide and 8 feet high, you have a total of 80 square feet. Deduct this area from the total wall area (from Step 2). In the example, this is 900 square feet minus 80 square feet for a net wall area of 820 square feet. You may calculate and deduct the area for doors and windows in the same way if you wish. However, the difference is usually small, so you can skip this step.

Find the number of concrete blocks required for 1 square foot of wall. Most concrete blocks are approximately 8 inches high by 16 inches long. Multiply the height by the length and divide the result into 144 (the number of square inches in a single square foot). For standard concrete block, this works out to 144/(8*16) = 1.125.

Multiply the number of concrete blocks per square foot by the net wall area. For our example above, this is 1.125*820 = 922.5 (round up to 923). Add 5 percent to allow for broken blocks and cutting to fit at corners for a total of 970 concrete blocks.