Garage sizes: single, double and triple

A garage is the only room in a house sized by an object that arrives after the walls are finished, cannot be cut down, and gets slightly larger every model year. That is why so many of them fail the same way: the car fits, and the person does not. Everything on this page is derived from two figures that no garage plan ever draws, the swing of a car door and the width of a person walking past a bonnet.

The two numbers on a garage plan, and which one you park in#

A garage described as 24 x 24 is quoted to the outside of the frame, because that is the number the builder prices, the slab is poured to, and the planner draws. The number that decides whether a car fits is the clear internal dimension between the finished wall faces. On a 2x4 stud wall with 1/2 in (13 mm) board on each face, each wall costs 4 in (102 mm), so a nominal 24 ft (7.32 m) becomes 23 ft 4 in (7.11 m) inside. A 2x6 wall costs 13 in (330 mm) across the pair. Where the code requires 5/8 in Type X board on the wall shared with the house, take another 1/4 in.

There is a second datum error underneath that one. Measure the internal width at 40 in (102 cm) above the floor, not at the skirting, because that is the height of a car's widest point and of the mirror. A garage measured at floor level can be 4 in wider than the same garage measured at hip height, once you count a boxed-in soil pipe, a stud that has bowed, or the electrical panel that has to keep its working space clear. The habit is the same one set out in how to measure a room properly: pick a datum, name it, and take every measurement from it.

Every size in the tables below is given as the nominal outside figure, with the internal clear beside it, because both are needed and they are never the same.

Width: two car bodies and three door swings#

Start with body width, excluding mirrors, because mirrors fold and doors do not.

A front car door needs about 30 in (76 cm) of clear space beside the body for an adult to open it fully and step out without turning sideways. That figure is derived on the car parking space and door swing page; take it here as a fixed cost per side.

The width of a garage is then body widths plus one more gap than there are cars:

• One mid-size sedan: 73 + 30 + 30 = 133 in, or 11 ft 1 in (3.38 m).
• Two mid-size sedans: 146 + 90 = 236 in, or 19 ft 8 in (5.99 m).
• Two full-size vehicles: 162 + 90 = 252 in, or 21 ft 0 in (6.40 m).
• Three mid-size SUVs: 225 + 120 = 345 in, or 28 ft 9 in (8.76 m).
• Three full-size vehicles: 243 + 120 = 363 in, or 30 ft 3 in (9.22 m).

Two things fall out of that arithmetic immediately. The first is that the standard 20 x 20 ft double, at 19 ft 4 in (5.89 m) inside, is four inches short for two sedans and 21 in (53 cm) short for two SUVs. The second is that the cost of a bay falls as bays are added, because the gaps are shared: a single bay spends 141 in per full-size car, a double spends 126 in and a triple 121 in. A third bay is the cheapest car space in the building.

The middle gap in a double is used by two doors, the passenger door of one car and the driver's door of the other, but almost never at the same time. Thirty inches still works. It stops working on the day four people arrive in two cars, which is the one scenario a garage is never planned around.

Depth: bonnet, tailgate and the door that has to close#

Depth is vehicle length plus two allowances that people habitually merge into one. In front of the bonnet, allow 36 in (91 cm), which is the primary walkway width used everywhere else in a house and the figure that also lets a 12 in (30 cm) deep shelf live on the end wall. Behind the tail, allow 24 in (61 cm) so the sectional door can close past the bumper and so you can get round the back with a bag of shopping. Twenty-four inches is a squeeze, and the reasoning behind both numbers sits in walkway and circulation widths.

A tow hitch adds 6 to 10 in (15 to 25 cm) and is invisible in every catalogue length. A bicycle rack on the tailgate adds 12 to 18 in (30 to 46 cm) and is the single most common reason a garage door will not close.

Adding a bench changes the depth by 60 in (152 cm), not by the depth of the bench: a 24 in (61 cm) top needs 36 in of standing room in front of it, and that standing room cannot be shared with the space the bonnet occupies. The heights and depths involved are set out in workbench height, depth and clearances.

From 12 x 22 to 36 x 24 ft, with both dimensions honest#

For comparison with the rest of the house, 545 sq ft is larger than most primary bedrooms and about the size of a small apartment, which is worth holding in mind next to the figures in standard and minimum room sizes.

Ceiling height, and the floor that is not flat#

Eight feet (2.44 m) is the working minimum, and it is not arbitrary: a 7 ft (2.13 m) sectional door needs 12 in (305 mm) of headroom above the opening for a standard torsion assembly, and 84 plus 12 is exactly 96. An 8 ft (2.44 m) door therefore needs a 9 ft (2.74 m) ceiling, and the whole chain of headroom, backroom and drive-through height is worked through in garage door sizes, headroom and backroom. A two-post lift needs 11 to 12 ft (3.35 to 3.66 m) to raise a sedan clear of a standing adult.

The floor is not level either. The IRC requires a garage floor to be sloped toward the door or a drain, and 1 to 2 per cent is normal practice. Over a 22 ft (6.7 m) depth, 1.5 per cent is 4 in (100 mm), which means the ceiling height at the back wall is 4 in greater than at the opening, the workbench on the back wall stands 4 in higher relative to the door threshold, and any full-height cabinet run needs scribing. The step up into the house is measured from the lowest point, not the highest, and that detail belongs with the garage to house door, step and landing.

Three worked plans: 14 x 26, 24 x 24 and 24 x 30 ft#

One car and a real workshop, 14 x 26 ft nominal. Inside, 13 ft 4 in x 25 ft 4 in (4.06 x 7.72 m). A mid-size sedan takes 73 x 193 in, leaving 87 in of width and 111 in of depth. Put a 24 in bench along the back wall with 36 in of standing room, and 24 in deep shelving down one side above 60 in. The car still opens both doors.

Two cars and bikes, 24 x 24 ft nominal. Inside, 23 ft 4 in square (280 in). Two full-size vehicles and three gaps use 252 in, leaving 28 in of width. That is not enough for floor storage, so bikes go on the side walls above the door swing, hung by the front wheel at 72 in (183 cm), following bike and sports gear storage dimensions.

Two cars and a gym, 24 x 30 ft nominal. The extra 6 ft of depth beyond the 24 ft the vehicles need gives a 23 ft 4 in x 6 ft (7.11 x 1.83 m) strip at the back wall, which is 140 sq ft (13 m2), enough for a rack and a platform provided the ceiling is 9 ft or more. That plan is worked through in garage gym layout dimensions, and the ceiling constraint usually decides it.

More of the numbers behind bays, doors and benches sit on the garage and workshop dimensions hub, and the conversions that make an imperial garage and a metric car disagree are collected in imperial and metric. If a figure needs converting quickly, the interior unit converter will do it without rounding a car into a wall.