What is a full bath? We all know bathrooms come in a number of sizes—full, half, and even three-quarter—but what do those other fractions correspond to? This is a common question among home sellers, especially when they're listing their home and deciding how to price it. So whether you're planning a remodel, looking to sell (here's how to find a real estate agent in your area), or just curious about how many bathrooms your home actually has, here's a primer on bathroom sizes.

What is a full bath?

A full bathroom is made up of four parts: a sink, a shower, a bathtub, and a toilet. Anything less than that, and you can’t officially consider it a full bath.

The math is simple: Each utility is counted as one-quarter, so you add and deduct a quarter for each one, as the case may be. Therefore, a bathroom with a sink, toilet, and shower is considered a three-quarter bath. A bathroom with just a sink and a toilet is a half-bath. A quarter-bath is quite rare for the simple (and hygienic) reason that if you have a toilet, you need a sink in which to wash your hands—and a room with only a sink is just plain odd.

Upgrading a shower, regardless of size or style, doesn’t change the count. Think that rain shower head is going to up the value of the bathroom? Maybe. But it won't up the count—the only way to do that is by adding another utility.

How much does a tub matter?

Many master baths today have only showers, and are therefore listed as three-quarter baths. Will that hurt your home’s selling price?

Probably not, especially if there’s a tub elsewhere in the house, says Ginny Ollis, a Realtor® with Coldwell Banker Residential Brokerage in San Diego. “Many homebuilders put only a shower in the master now," she says.

But some experts say a lack of a tub can be a deal breaker. “There must be a tub in the house,”says Kathryn Bishop, a Realtor with Keller Williams Realty in Studio City, CA. “I've seen buyers walk away because only showers are available. Where do you wash the kids?”

The bathroom count counts

Bishop says, overall, a home’s bathroom count is important to buyers.

“Bathroom count and bathroom size—full, three-quarters, or half—are extremely important to all my buyers. More family quarrels occur when the bathroom accommodations don't fit the family's needs, and my buyers are very aware of that," she says.

So get real: If you've ever shared a bathroom with someone else (especially those of you who have teenagers!), you know that the number of bathrooms in a household matters nearly as much as the number of bedrooms.