Cutting concrete blocks can be done a few different ways. The easiest would be with a circular saw and a masonry cutting blade. It will provide a perfect cut but is very dusty, so be prepared for a bit of cleanup and the need for wearing face dust masks. This "how to" will show a manual method of cutting concrete blocks with a chisel and hammer. Note that cutting concrete blocks should be used as a second best option to buying smaller blocks or blocks cut to size by a professional at a hardware type of store that specialises in masonry.
Find a concrete block that is meant to be cut. It will have a vertical concrete bar in the middle.
Lay concrete block on the ground or sturdy work area.
Draw a line on one side of the block where you need the cut. Use a ruler as a guide for a straight line.
Turn the block over. Draw a line where you need the cut. Use a ruler as a guide for a straight line. Be sure it is in the exact same position as the line made on the opposite side in Step 3.
Strike the chisel on to the line in Step 3 with a bricklayer's or masonry hammer a few times across the line (not in the same spot or it will crack the block).
Turn the block over. Strike the chisel on to the line in Step 5 with a bricklayer's or masonry hammer a few times across the line (again not in the same spot or it will crack the block).
Listen for a ringing sound when you hit the block.
Continue hitting the line with the chisel and rotating sides for an even break.
Continue hitting the line with the chisel until the ringing sound turns flat as the crack grows.
Hit it all around the line once more and the block should part.
Sand the broken edge if it is too jagged.
Always wear safety glasses because jagged piece of concrete might fly into the eyes. Gloves are optional but recommended as they will provide a better grip on the chisel and hammer. Face or dust masks are recommended when cutting block, especially when cutting with a circular saw.