The most common regret we hear is not about color or price. It is "I wish I had gone bigger." A metal building is hard to expand once it is up, so sizing it right the first time is worth a little planning.
Start with what goes inside
List everything the building will hold, not only your vehicles:
- Cars, trucks, a boat, an RV or a trailer
- Workbench, tool chests, shelves
- Lawn equipment, ATVs, a tractor
- Storage, seasonal items, a freezer
- Room to open car doors and walk around
Measure the biggest items first, then add working space around them.
Common sizes and what fits
These are general starting points. Your use may need more.
| Size | Typically fits |
|---|---|
| 12x21 | One vehicle or small truck, light storage |
| 20x20 | A tight two-car garage |
| 20x21 | Two cars, or a small RV |
| 24x30 | Two cars plus storage |
| 24x36 | Two cars plus a workbench |
| 30x40 | A workshop or three cars |
| 30x50 | Shop plus an RV bay |
| 40x60 | Barn, four cars, or a barndominium |
Browse sizes in our size guide, including 24x30 and 30x40 pages.
Rules of thumb that save money later
Allow door-opening room
Plan roughly three feet or more of clearance on the side of each vehicle so doors open fully and you can walk past.
Add depth for storage
If you want shelves or a workbench along the back wall, add several feet of length beyond the vehicle.
Think about height
Standard sidewall height works for cars and trucks. Taller sidewalls help if you want:
- An RV, a camper or a tall trailer
- A vehicle lift
- A loft or mezzanine
- Large equipment
Check the clearance of your door as well as the height of the building.
Size the doors to your biggest vehicle
Door width and height must fit your largest vehicle comfortably. Roll-up doors come in several sizes.
Plan for growth
If you may buy another vehicle, start a hobby or add equipment, build slightly larger now. The cost per square foot of adding a few feet is usually lower than building a second structure later.
Match the size to your land
Before choosing, check:
- Setbacks and easements that limit where you can build
- Maximum accessory building size under local zoning (see do you need a permit)
- Slope and access, so delivery and installation can reach the spot
- Space for the slab, which must match the building size (see slab requirements)
Size and price
Larger buildings cost more, but the price is not simply linear. Height, doors, certification and finishes all matter. Our guide to what drives metal garage cost explains the factors.
Carport or garage first?
If you are not sure whether you need an enclosed building, read metal carport vs metal garage.
FAQ
Is a 20x20 enough for two cars?
It fits two standard vehicles, but space is tight and storage is limited. Many buyers choose 24x30 for extra room.
How many cars fit in a 30x40?
Commonly three, or a workshop plus vehicles, depending on vehicle size and how much storage you add.
Can I make a building longer later?
Sometimes, but it depends on the design. It is usually simpler to choose the right size at the start.
What size do I need for an RV?
Check your RV's height, width and length, then add clearance. Many owners choose a taller sidewall and a wider door.
Not sure? Tell us what you are storing and your specialist will recommend a size.