Every builder knows entry doors come in standard sizes, allowing them to frame in rough openings beforehand. On rare occasions, plans call for one or more custom doors. While it’s usually easy to make a standard door smaller to fit a non-standard opening, you usually must special-order the door if you need a larger one.

Garage doors also come in standard sizes, but they’re much more difficult to modify on site. And if they’re steel, vinyl or fiberglass, modification isn’t even possible.

While you can order a garage door to fit a non-standard opening, it ends up being lot more expensive than one with standard dimensions. If you’re building a new garage or modifying an existing one, you probably want to avoid that extra expense unless you need extra space for a boat or RV.

You also need a grasp of standard garage door sizes if you’re replacing an existing one. A garage door upgrade is one of the best things you can do for your home’s appearance. But if you have a non-standard opening, be prepared to spend more.

Also check out these six best Wi-Fi garage door openers to retrofit your old opener.

How to Measure for a Garage Door

Most garage doors must fit exactly inside the door opening, so determine the width and height with a tape measure. If the door has a track system, you’ll need space between each side of the door and the wall for the springs.

Most track systems require 3-3/4-in. of room on each side, but some can take up to 5-1/2-inches. Moreover, most doors that open vertically need 10 inches of headroom between the top of the opening and the ceiling, and some require 12 inches.

If you’re in the middle of construction, don’t forget to allow for trim when you measure the width and height of the door opening. Standard 3/4-in. trim material will reduce the width of the opening by 1-1/2-in. and provide an extra 3/4-in. of side room. If the opening is already trimmed out, you don’t need to make this allowance.

Standard Garage Door Size: Single-Car Garage

Doors for single-car garages come in four standard widths: seven, eight, nine and 10 feet. Most cars are five feet two inches to five feet 10 inches wide, so an eight-foot door is usually more comfortable than a seven-foot one.

You’ll probably prefer the seven-foot door if you’re storing lawn tools or a golf cart in your garage. You might want a nine- or 10-foot door if you’re parking your car as well as storing tools, or if you have a larger vehicle.

The standard heights are seven and eight feet. The most common standard size for a single-car garage door is nine feet wide by seven feet high.

Standard Garage Door Size: Two-Car Garage

The standard dimensions of a two-car garage door are 16 feet wide by seven or eight feet high.

Instead of a 16-foot door, many homeowners opt for two eight-foot doors separated by a central column. This arrangement provides more structural stability, because the column supports the door header, and two smaller doors have less visual impact than one large one.

If you want the doors to open automatically, you’ll need two openers or a tandem opener that operates both doors at the same time.

Standard Garage Door Size: Triple-Car Garage

Manufacturers offer triple-wide garage doors that are 32 feet wide by seven or eight feet high. That might seem excessive for a garage that only accommodates one extra vehicle, but the extra width provides space between the cars for people to get in and out.

Not surprisingly, doors this wide aren’t common. Construction calls for expensive oversize headers, and such a large door facing the front of the property can have a negative impact on curb appeal.

One alternative: Install double-wide and single-wide doors next to each other. Or go with three single-wide doors separated by wide columns to provide space between vehicles.

Standard Garage Door Size: RV Garage

Manufacturers offer doors for RV garages that are 12 feet wide and 14 or 16 feet high. RVs come in all sizes, but all will fit inside a 16-foot-high door.