Step 1
Measure the height of your counter from its bottom edge. Subtract 10 to 12 inches from the bottom edge of the counter to determine the ideal height for your seat. Give yourself slightly more leg room if your counter has a large overhang.
Step 2
Select chair legs designed for "bar height" tables, if your counter is 40 to 42 inches high. Opt for "counter height" chair legs if the counter is 35 to 36 inches high. Use "extra-tall" or "spectator" chair legs for a table that is 45 to 48 inches tall. Select a material and color that coordinates with the chair plan. Opt for a swivel-style chair base if you prefer to move while sitting.
Step 3
Detach the standard-length legs from your chair, either unscrewing them by forcefully turning the leg or sawing them off with a hand saw. Sand and varnish or paint the chair, if necessary, while it is detached from its base. Start with heavy gauge sandpaper and progress toward finer paper. Finish sanding with moistened, very fine sandpaper for a glossy look. Follow the manufacturer's instructions completely for all drying times of any paint or varnish.
Step 4
Work with another person to hold the chair atop your new, counter-high chair legs in order to test the height. Measure the distance from the seat to the bottom of the counter to confirm it is sufficient. Screw a thin shim of wood to the bottom of the seat if the new legs are not quite long enough. Sand down the exposed side of the shim for a smooth finish. Attach the legs to the base of the seat or the shim using the drill.