Minimum Size for an Under-Stairs Toilet

Minimum Toilet Size

• When choosing a toilet for your half bath, look for standard round toilets rather than those with elongated bowls that eat up space. The smallest toilets available, according to This Old House, extend only 20 inches from the wall and use 1.6 gallons per flush. Another option to consider is a wall-hung toilet. Because the tank is concealed, the bowl only extends about 15 inches from the wall.

Toilet Space Requirements

• As you design your half bath, you'll need to keep in mind the International Residential Code regulations regarding minimum clearance space. Measuring from the center of the toilet to the closest side wall, you must have at least 15 inches of space. From the front of the toilet bowl, you must have a minimum of 21 inches of open space in front of the toilet. So, for just the toilet, the room will have to measure at least 30 inches by 21 inches, plus the size of your toilet -- a minimum of 15 to 20 inches.

The Sink

• Regulations require you to have a sink in each bathroom. A small sink will extend about 11 inches from the wall. The International Residential Code states you must have 21 inches of floor space in front of the sink. This space does not have to be in addition to the clearance space in front of the toilet. The two clearance spaces can overlap.

Smallest Space Requirements

• Taking into account the toilet size, the clearance spaces in front of the toilet and the size of the sink, the smallest your half bath could measure is 30 inches wide by 47 to 52 inches in length. This is approximately 11 square feet. This measurement may need to be larger if you have a door that swings into the bathroom. As with any project, check with your local jurisdiction's regulations and permit department before you begin.