ROOM OF THE DAY Room of the Day. If you CAN add this powder room in this small space insulate the walls for sound use a solid core door muffles the noises and install a good exhaust fan. Small Powder Room Floor Plan Powder Room Small Bathroom Floor Plans Basement Bathroom Design Powder Room Layout Standard size of 20 square feet with smaller powder rooms being allowed as small as 11 square feet. What is the smallest a powder room can be . According to the International Residential Code IRC a powder room can be as small as 11 square feet. The smallest size possible is 11 square feet. An 8-by-5-Foot Bathroom Gains Beauty and Space. A powder room may need to fit in a narrow space under stairs or both. At least 21 in front of the toilet and sink for leg room. Considering this what is the minimum width for a powder room. Toilet and sink must be 15 apart. Minimum of a 32 opening for a door. At least 21 in front of the toilet and sink for leg room. I really want