It can also be helpful information when you are buying or selling a house and are evaluating the efficiency of the plumbing fixtures. 06 of 06. Measure straight down from the center of the overflow to the point at which the drain is mounted to the tub: depending on what's easiest to get to, you can measure from outside the tub down to its underside, or from inside the tub to the tub floor. Our bathtubs come in a wide range of sizes, shapes, configurations and depths ensuring that you can find the right tub for your needs. Stand in front of the bathtub, like you were about to get in. This will help you determine the appropriate size for your bathtub. It can be a critical factor in choosing the size for a new water heater, whether it's a tankless or traditional tank-style model. You need to start with the top of the tub and measure the width of the tub from one end to the other. Select the appropriate thread attachment. Make sure you’re measuring from the outside of your tub, not from the inside. Measure the perimeter of the shower tile area if you plan to use border tiles. ... For most of the world, it's probably in Liter, a standard unit to measure capacity or space or volume. Use the old fitting to determine the size of your drain. For example, divide length-of-land / length-of-bathtub, and width-of-land / width-of-bathtub. Measure straight down from the center of the overflow to the point at which the drain is mounted to the tub: depending on what's easiest to get to, you can measure from outside the tub down to its underside, or from inside the tub to the tub floor. But if you don't love the idea of giving up baths in your small bathroom, this size is your best option: Length: 54 inches. Next, measure the width of your tub from the back wall to the front with the same techniques for the length. When you are installing a new bathtub surround, you want to make sure that you are getting the measurements just right.If you are tiling, and you don't measure it correctly, you can end up with big problems. Do not follow the curve of the tub; measure straight down. Do not follow the curve of the tub; measure straight down. Thankfully, there is a simple way to get the measurements. ... Charity. My home was built in '54, it is a cape-cod style home with a VERY small bathroom, which I am in the process of remodeling.