One drawing for each thing you need to measure, plus the one that catches most people out. A tape measure and ten minutes is all this takes. Measure the opening itself, never the old door, and write the numbers down before you start typing.
How to measure your garage in ten minutes
This is the same order a technician does it in. Work through it once, write the numbers on the back of an envelope, and you will have everything this tool needs and everything a quote is built from.
What you need. A tape measure, a pen and paper, and a step ladder if anything above the opening is out of reach. A second pair of hands makes a double door far easier. Do it with the door closed, in daylight if you can, and stand inside the garage rather than out on the driveway.
- Clear the opening first. Move the recycling bin, the bikes and the snow shovels out of the way, and sweep the concrete under the door. You are measuring to the concrete, not to a mat, a strip of carpet or a layer of leaves. Five minutes here saves you measuring twice.
- Width, three times. Measure straight across the opening, edge to edge, at the bottom, at the middle and near the top. Write all three down. Openings settle and almost none of them are perfectly square, and the door has to pass through the narrowest of the three, so the smallest number is the one that counts. If they differ by more than half an inch, say so on the form above and we will bring a level.
- Height, three times. Measure from the concrete up to the underside of the top of the opening, on the left, in the centre and on the right. Smallest number again. Do not measure the old door: doors are ordered to the opening, and a strip of trim hiding a gap is exactly how people end up with a door two inches too small.
- Floor to the lowest thing above the opening. Stand the tape on the concrete and run it straight up. Not to the ceiling, to the lowest thing above the opening: a joist, a duct, a water pipe, a light fitting, the rail of the existing opener. Walk the full width of the opening and keep the smallest number you get. We take the height of the door off that figure and what is left is your headroom, which is what decides which of the three track systems you need. It is worth doing twice.
- Sideroom, both sides. From each edge of the opening out to the side wall or the first thing in the way, measured at about the height of the opening rather than down at the floor where a bench or a step can fool you. Do the two sides separately, because they are very often different. The vertical tracks bolt into solid wood here, so drywall over a stud counts and drywall over nothing does not. If you are hoping for a wall mount opener, note whether either side has about 10 inches of clear wall, because that is what one of those mounts in.
- Backroom, at door height. From the wall the door sits in, straight back into the garage, to the first thing in the way at roughly the height of the open door. A shelf unit, a water heater, a ceiling mounted furnace or a low soffit all count, and all of them are easy to miss because you are used to walking round them.
- Take four photographs. The opening from outside, the opening from inside, the area above the opening, and the wall on the tighter side. Photographs settle more arguments than measurements do, and they cost nothing.
What the numbers are actually for
Width and height decide the door. Garage doors come in a ladder of standard sizes, 8, 9, 10, 12, 14, 15, 16 and 18 feet wide in 7 and 8 foot heights, and if your opening lands on one of those it can be ordered off the shelf. If it does not, the door is custom, which is routine but costs more and takes longer to arrive.
Headroom, sideroom and backroom decide the hardware. They have nothing to do with the door itself and everything to do with the tracks it runs on, which is why a garage can be perfectly ordinary from the driveway and still need a different track system once you look above the opening. Headroom is far and away the one that changes the answer.
None of these are guesses on our side. The clearance figures this tool works from are the same ones the manufacturers publish, and they are set out in full in our guide to headroom and the track types that suit it. The sizing ladder and the rough opening convention are covered in garage door sizing, measured properly.
The three mistakes that cost people money
- Measuring the door instead of the opening. The most expensive one, and the most common. If the old door looks small and there is trim around it covering a gap, the opening is bigger than the door and always has been.
- Measuring up to the ceiling when something hangs lower. A duct, a beam or the opener rail hanging six inches below the ceiling is what the track has to clear, so the ceiling is the wrong thing to measure to. This is the single most common reason a job changes on the day.
- Measuring backroom to the back wall. The workbench, the shelving or the water heater is what stops the door, not the wall behind it. Measure to the first thing in the way, not to the far end of the garage.