Next to the number of bedrooms, the number of bathrooms in a house is a huge selling point. But when perusing home listings, you’ll quickly realize that bathroom math isn’t so simple.

For example, you may see that a particular place may be listed as having two full bathrooms and one half-bath. But what is a half-bath, exactly? Or a quarter-bath, or three-quarter bath, or “full bath” for that matter?

Let’s run through the numbers! Bathroom numbers, that is.

What is a full bathroom?

First, let’s start with the whole caboodle: a full bathroom. In order for a room to be listed as a “full bath,” it must contain four key fixtures: a toilet, sink, bathtub, and shower (or shower/bath combo). A full bathroom off the master bedroom is one of the most desired features by today’s home buyers, according to a survey conducted by the National Association of Home Builders. Other features that are popular in a full bath but are not necessary for that designation include a linen closet, bidet, makeup station, and/or double sink.

What is a half-bath?

A half-bath, also known as a powder room or guest bath, has only two of the four main bathroom components—typically a toilet and sink. The half-bath is generally located on the main level of a multistory home, and is used by guests who come by to visit for a few hours, or by those who don’t want to run all the way upstairs when nature calls.

Most real estate agents will tell you that adding a half-bath to your home is one of the most profitable home improvements you can make.

“If you spend about $4,000, and that’s really all it should cost to convert a [coat or storage] closet to a half-bath, that and more will definitely come back to you when you sell your home,” says Realtor® Jennifer Niman of Berkshire Hathaway HomeServices.

What is a three-quarter bath?

You’ve probably figured out by now that a three-quarter bathroom lacks one of the four fixtures listed above. That would most commonly be the tub. A three-quarter bathroom most often has an upright stall shower, a sink, and a toilet. But in older houses or condos, a three-quarter bath might have just a sink, toilet, and tub, but no shower. In this case, the new owner almost always converts it to a full bathroom by installing a shower head over the tub, and enclosing it with a shower curtain. That’s an easy and inexpensive way to do a quick upgrade, especially if the walls around the bathtub are already tiled.

What is a quarter bath?

And finally, what of the humble quarter bathroom? A room with just one of the four elements—typically a toilet. Quarter bathrooms are rare for good reason: Who doesn’t want to wash their hands after attending to their business? Another type of quarter bathroom is just a shower, often located out by a pool to rinse off.

Do two half-baths equal a whole?

If a home is listed as having three bathrooms and two half-baths, why don’t they just add them all together and say that there are four bathrooms? That would seem logical, but each bathroom must be listed separately, because this gives home buyers a better sense of the home’s features and their options when they’ve gotta go.

Published by Lisa Johnson Mandell on realtor.com.