Measure out the size of the fire pit on the lawn. A standard fire pit size is about 4 feet square so that it is not too large to tend easily without reaching far into the fire pit. Using 9-inch-long fire bricks will require six bricks per side to achieve 54 inches on each of the four sides. Mark the area with string.
Cut the sod in the area out with a shovel by cutting at an angle to remove the grass and sod down to about 2 inches below ground level. Fill the depressed area up to the ground level with sand and spread evenly. Sand helps for drainage purposes so that rain or any other water will drain off the area.
Place the first layer of fire bricks in a square around the four sides, leaving a small gap between each fire brick. This will provide the necessary air gaps for fires to burn well.
Place the second layer of fire bricks on top of the first layer. Add as many additional layers as you need to achieve the desired height. Taller retaining walls will keep sparks and shifting logs at bay better than short retaining walls.
Mix concrete mix according to the manufacturer's instructions on the package. Apply to the outside of all layers of brick with a trowel. Take care not to cover the air gaps in the first layer.
Place a metal fire bowl in the middle of the fire pit by removing some of the sand in the middle of the pit and pressing the bowl down firmly so that it sits level. This construction method of a fire pit does not require a fire bowl, so you can omit this step if you do not want to use a fire bowl.