Will A King Size Mattress Fit In A King Size Waterbed Frame

Generally a king size water bed measures more along the size of a california king size mattress that measures approximately 72 x 84.
Will a king size mattress fit in a king size waterbed frame. Or that you have to go one size down and purchase a full size mattress. Of course your bed will no longer be heated as your waterbed mattress heater is for waterbed bladders only. Waterbed mattress inserts are oddball sizes. A hardside and softside california waterbed mattress measures 72 inches wide by 84 inches long and matches the dimensions of a hardside king waterbed mattress.
Likewise for a queen size mattress. Sizing the cal king. A standard king size measures. Some people believe that to get a regular mattress to fit a waterbed frame that a queen size would fit.
Whether your existing hardside is a queen king single or california king because of the dimensions needed to fit a waterbed bladder the size of a replacement insert mattress will not be. Both of these are incorrect and will not fit properly. Twin full queen or king waterbed frames even those with hard sides can accept a new. It will have to be ordered.
Set a conventional all in one mattress inside the waterbed frame the same size as the waterbed mattress. If so it would be a tight fit.