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Size is not just width and height on an order form. It is the finished opening, the space above it, the space beside it, and the depth inside the garage. Get those four right, and a standard door will fit cleanly. Miss one, and even a correct width can fail on track clearance or spring placement. This post explains single, double and custom openings, and how to measure each one before you order.
Single openings, in plain terms
A single opening serves one vehicle bay. Common widths are 8, 9 and 10 feet, and common heights are 7 and 8 feet. An 8 foot wide door suits a compact vehicle and a tight bay, but mirrors and door swing need care. A 9 foot wide door is a comfortable middle choice for many sedans and SUVs. A 10 foot wide door helps a full size truck, a vehicle with wide mirrors, or a driver who wants extra margin when parking.
Height is often overlooked. A 7 foot tall door suits most passenger vehicles. An 8 foot tall door helps taller SUVs, trucks, roof boxes, and work vehicles with racks. Measure the tallest vehicle you will actually park inside, including any roof load, and add clearance for the door panel and the opener rail. A door that clears the vehicle by a finger width will feel tight every day, and a rack left on top can turn a tight fit into a scrape.
Double openings, and the two door alternative
A double opening serves two bays with one wide door. Common widths are 16 and 18 feet, with heights of 7 and 8 feet. A 16 foot wide door is the usual double choice, while an 18 foot wide door gives more room for two wide vehicles side by side. A double door gives a broad, unbroken front, and it needs only one opener, but the panel is large and heavy, and spring and opener sizing must match that weight.
Two single doors are a real alternative, and they change daily use. Each bay gets its own door and opener, so one vehicle can come and go without opening a wide panel, and a damaged panel affects only one bay. The trade off is a center post between the doors, two openers to maintain, and a front that reads as two panels rather than one. If you often use only one bay, or you want repair flexibility, two singles may suit you better than one double.
How to measure without guessing
Measure the finished opening, not the rough framing, and measure in more than one place. Width can vary from top to bottom if framing is out of square. Height can vary from side to side if the floor slopes. Record the smallest width and the smallest height, because the door must fit the tightest point, not the average.
Next, measure headroom, side room and backroom. Headroom is the distance from the top of the opening to the ceiling or the lowest obstruction above it. Side room is the distance from each side of the opening to the nearest wall or obstruction. Backroom is the distance from the opening into the garage, along the ceiling, to the back wall or the first obstruction. A door that fits the opening but lacks track room will not open fully, and a track that fouls a light, a duct or a storage rack will cause trouble from day one.
When a custom size makes sense
Custom sizes make sense when the opening is not a standard width or height, when a tall vehicle needs extra height, or when an older home has a bay built for a smaller vehicle era. A custom door is built to the finished opening, rather than forcing a standard door into a gap with filler panels. That fit can look cleaner, seal better, and avoid a patchwork of trim around the edges.
Custom also brings trade offs. Lead time is usually longer, panel and window choices may be narrower, and a future replacement will need the same custom size again. Before ordering custom, check whether a small framing change could bring the opening to a standard size, and whether that change is worth the extra work. Sometimes a standard door with careful trim is the better long term choice, because the next replacement will be simpler.
Clearance traps that catch buyers
Four traps appear again and again. First, a low ceiling with a tall door leaves no room for a standard track, and a low headroom track or a different opener layout may be needed. Second, a beam, duct, light, or storage rack in the track path blocks travel, even if the opening itself is fine. Third, a sloping drive or garage floor changes the seal gap at the bottom, so a door that looks level at the top may draft at one corner. Fourth, a vehicle that fits today may not fit after a roof rack, a lift, or a larger replacement vehicle, so measure for the vehicle you plan to keep, not just the one you own now.
The International Residential Code treats garages and carports as a distinct section, and it sets rules for the garage and house separation, including opening protection between a private garage and a sleeping room (International Code Council). That code point is not about door width, but it is a useful reminder to check local rules and permits before changing an opening, a header, or a wall between garage and house.
Choosing between standard and custom
Start with the finished opening and the vehicle plan. If the opening matches a common size, and the vehicle plan fits that size with margin, a standard door is usually the simplest choice. If the opening is between sizes, or the vehicle needs height that a standard door cannot give, custom is worth the lead time. In both cases, get the door size, track type, headroom, side room and opener plan in writing before ordering, and check them again when the door arrives.
A final check helps. Stand in the garage with the tape in hand, look at the track path from floor to ceiling, and picture the door open, with panels stacked overhead. If anything in that path looks tight, raise it at measuring time. A question asked early costs minutes. A track problem found on install day costs a reschedule.
What to check next
Read the new garage door installation page for measuring and install day detail, and the garage door replacement page if you are swapping an old door in an existing opening. Then visit the areas hub to see the places covered by this referral service.
Sources
- International Code Council, 2018 International Residential Code, garages and carports
- International Code Council, 2018 International Residential Code, building planning
Common questions
What is the most common single garage door size?
A single door is often 8 or 9 feet wide and 7 feet tall, with 9 feet wide giving more side clearance for a wider vehicle or for mirrors. Older garages may have narrower openings, so measure the finished opening rather than assuming a standard size. Height matters too, especially for taller vehicles, roof racks, or a vehicle with a tall load.
Is one double door better than two single doors?
Neither is always better. One double door gives a clean front and one opener, but it is wider, heavier, and harder to use if only one vehicle needs access. Two single doors give separate control, more flexibility, and a smaller panel to replace, but they need a center post and two openers. Choose from daily use, front design, and repair flexibility.
Can I widen an existing garage opening?
Sometimes, but widening is structural work, not just a larger door order. The header, framing, and wall finish may need changes, and local code and permit rules may apply. Ask the provider what the opening can support, what framing changes would be needed, and whether a permit is required before you order a wider door.
Why do headroom and side room matter?
Headroom is the space above the opening for tracks and springs, and side room is the space beside the opening for vertical tracks. Without enough of either, a standard track may not fit, and a low headroom track or a wall mount opener may be needed. Measure both during the first visit, not after the door has been ordered.