Select a flat work surface that is a comfortable work height. Place the bar stool on the surface.
Examine the stool for uneven leg lengths. Use a shim underneath any leg that is not the same length as the other legs. A shim could be a skinny piece of wood or folded paper.
Cut a block of wood 1-inch high. Make certain the bottom and top of the block are flat.
Place the block against the bottom of the leg. Use the top of the block as a guide and mark the chair with a pencil.
Rotate the block around the bottom of the stool leg and continue to mark the legs with a pencil. Mark all the legs using this method.
Lay the stool on its side and use a handsaw to trim the legs at the pencil lines.
Remove rough edges with medium-grit sandpaper.