A new toilet can liven up your bathroom, but only if it fits. Nobody wants to buy a brand new toilet and haul it home only to find it doesn't fit the bathroom. By measuring the "rough-in" distance of your old toilet before buying a new one, you can guarantee your new toilet will fit properly. You can learn how to measure your toilet in just a few quick steps.
Locate the closet bolts on your old toilet. Also called hold-down bolts, these are at the base of the toilet and mount the toilet to the floor. Depending on your toilet, you may have one or two bolts on each side.
Measure your old toilet's "rough in," which is the distance from the drain pipe to the back wall behind the toilet. Remember not to include the baseboard thickness in your measurement. Use your tape measure to determine the distance from the wall behind the toilet to the center of one of the closet bolts. If you have two closet bolts on each side, measure to the center of the rear bolt. For most toilets this distance is 12 inches. You new toilet must match your old toilet's rough in.
Measure the distance from the closet bolts to the back of the tank on your desired toilet. This gives you the length of the base of your new toilet. Compare that measurement to the rough in of your old toilet. If the base of your new toilet is equal to or smaller than your old toilet's rough in, you should have no problems making the new toilet fit.
Measure from the sides of the closet bolts to the side walls or other objects in your bathroom. This gives you the amount of side-to-side clearance you have for your new toilet. Just because the bolts may line up on your new toilet, doesn't mean it will actually fit in the space, so make sure to take this measurement.
Decide between a round or elongated bowl. If you have a small bathroom, stick with a round bowl as elongated bowls are typically about 2 inches longer than a round bowl.