A standard toilet flange is three or four inches in diameter. This will ensure a tight, secure seal between the toilet and the drainage system, as well as support the weight of the toilet and prevent leaks.
Toilets with wider or narrower flanges may not provide as perfect a seal or as much stability, making them ineffective. Measure your drain pipe carefully to ensure it will fit properly, or find out how large your current flange is if you will be replacing it entirely.