Bathroom fixtures come in a variety of stock sizes. Standard tubs are usually 30x60-inches. Whirlpool tubs are often 32x60-inches. The typical shower is 32x32-inches. Toilets vary a lot in size, but the rough-in opening is usually 12-inches from the wall. Bathroom cabinets are usually between 18 and 20-inches deep. They come in a range of widths, depending on whether they are single-sink or double-sink vanities.
Standard sizes allow manufacturer's to produce units more efficiently. The lower the production cost, the lower the cost to the end consumer. Many stock cabinets come with coordinating wall cabinets that can be installed extra storage.
Finding the Best Layout
Draw a detailed floor plan on .25-inch graph paper. The scale should be 1-inch to 1-foot. Indicate every wall, window, and door opening. Account for the current plumbing, because changing the plumbing can be costly. Remain open to a new layout. If the functionality of the bathroom is improved, the changed will pay for themselves when it's time to sell.
Make scaled paper cutouts of all fixture, such as toilets, tubs, showers, and cabinets. Identify each cutout. Play with different options, keeping in mind that you need at least 24-inches in front of the toilet. Use 2-foot deep cabinets for linen storage if floor-space allows. You will need between 60 and 72-inches for a double vanity; otherwise, the space is too crowded for more than 1 person. 30-inches is the standard space beside a tub. 12-inches on each side of the toilet is more comfortable than a narrower space.
When you are through playing with your options, you will know which fixtures will fit into your bathroom design. Then it’s time to go shopping for the best values.