You’ve heard the expression, “measure twice, cut once” when it comes to home improvement? The same adage holds true for kitchen and bath fixtures and accessories: measure twice, buy once.

For the most part, figuring out the size fixture you need is about measuring from the center of one bolt the center of the opposite bolt. This rule-of-thumb especially applies to faucets where the difference between an 8-inch widespread and a 4-inch center set is significant in both the kitchen and the bathroom.

Replacing your kitchen sink means measuring opposite what probably feels more natural when you’re standing in front of it. Instead of the length being the side-to-side measurement, it’s actually the front-to-back measure, and the width is from wide-to-side.

Sinks also come in different depths so shoppers should be aware of how much they’ll have to bend to reach items on the bottom of their sinks.

Moving into the bathroom, unless you’re gutting the entire space and starting fresh, knowing how much room you have for your bathtub is paramount to a (relatively) stress-free installation.

Whether you’re going with a new stand-alone tub or a shower-over-tub configuration, you have to measure front-to-back and side-to-side. For a stand-alone tub, there’s a little more leeway depending on the traffic pattern of the bathroom; maybe there only needs to be a few inches of clearance on the two sides instead of three.

For a shower-over-tub, though, a 32-inch wide tub will not – no matter how hard you try – fit into a 30-inch space. Likewise, the most common size for a bathtub is 60 inches long, and because these tubs are designed for snug spaces, measurements have to be accurate.

Get the perfect fit with your new toilet by getting the rough-in measurement correct the first time. Measure from the wall behind the toilet to the center of floor drain. 12 inches is the most common toilet rough-in measurement, but if you live in an older home, also take the measurement of the wall to the center of the closet bolts.

For smaller bathrooms, measuring from the center of the closet bolts to the walls and/or vanity on either side of the toilet is also necessary so you know the space in which you have to work.

Towel bars are another item where measuring between the centers of the bolts determines the size you need. Instead of returning a product you thought would fit or just making do with what you get, take a second to consider the difference between an 18-inch bar and a 24-inch bar and order accordingly.

Where you place a towel bar or towel ring is equally important. For bath towels, a general rule to follow is to place them at least 48 inches above the floor. At this height, towels folded over the towel bar will more than clear the floor but aren’t too tall for little ones to reach.

Rings, which are most often used for hand towels, should be installed within easy reach of the sink. Hanging one above a sink and/or vanity requires at least 18 inches of space from the top of the surface to the center of the ring’s bolt. This will give a hand towel plenty of room to hang without interfering with anything stored on the deck of the sink or vanity.