Cake layers don't need to be perfectly level to taste delicious, but it looks much more impressive if you cut into a cake and the layers are even. Cakes often bubble in the center as a result of uneven cooking, so the domed top must be removed so the layers stack level. Additionally, a thick cake can be cut in half to create two layers with a layer of frosting in between -- more frosting is a good thing. A long, serrated knife or a wire cake leveler can be used to cut level layers.
Set the cooled cake on a flat cake plate -- avoid dinner plates with raised edges. If available, set the plate on a lazy Susan or rotating cake plate. You can turn a cake plate without a lazy Susan, but it makes it easier.
Place a long, serrated knife flat at the lowest point on the top of your cake, right at the edge of the cake. While wrapping a cake pan with wet towels while baking can help the cake to bake level, many cakes have a slight dome at the top which is a common side effect of uneven cooking.
Measure the cake with a ruler and divide this measurement in half to find the total thickness needed for each layer when cutting a cake in half crosswise. Slice into the cake slightly at the halfway measurement with a serrated knife to mark the cake.
Rotate the cake a quarter turn, place the ruler against the cake and make another small slice. Repeat this process until you have a total of four evenly spaced cut marks at half the height of the cake.
Position the knife at one of the cut marks and hold the blade so it's perfectly level. Move the knife back and forth in a sawing motion while slowly rotating the cake plate to connect the four slice marks into one continuous mark around the cake's circumference. You don't want to cut too far into the cake, but instead focus on ensuring the blade connects each slice mark evenly.
Cut through the cake while holding the knife perfectly level. Rotate the cake plate slowly while cutting so you can constantly use the slight cut line as a cutting guide. Continue cutting until you reach the center of the cake and the two layers are cut in half. As an alternative to a serrated knife to complete the cut, you can cut a piece of plain dental floss, fishing line or thread longer than the cake diameter and pull it through the cake while using the cut around the circumference as a guide. This works much like a cheese slicer and results in fewer crumbs than using a knife.
Remove the domed cake top with the serrated knife, cutting through the top at the lowest point around the top cake edge.
Measure the height of the cake and divide by two to find the necessary height at which to cut the cake.
Stand a large cake leveler against the side of the cake and adjust the horizontal wire up or down so it falls at half the height of the cake. Cake levelers have notched legs and you simply place the wire ends in the corresponding notches.
Move the cake leveler back and forth in a sawing motion to cut into the side of the cake. Keep the leveler standing upright while you saw so you don't end up with uneven cake layers.
Slide the cake leveler to the opposite side of the cake so the wire cuts the cake in half. This works much the same as cutting a cake with dental floss or thread, but the wire is set at a fixed position on the legs to ensure the cake is cut perfectly level.