Before you call
How do I measure my garage floor?
Measure the concrete rather than the building: wall to wall one way, back wall to the outside edge of the door opening the other, and multiply.
The short version
- Measure inside the walls, not outside the siding.
- Measure to the outer edge of the door opening, because the slab runs out to it.
- Add any apron, step or landing that would get coated with the floor.
- Note the door openings, the floor drain if there is one, and any step down into the house.
The measurement itself
Stand at the back wall and measure across to the far wall, then from the back wall out to where the concrete ends at the door. Multiply the two. That is the floor, and it is usually bigger than people guess, because a stall is deeper than it is wide and the depth is the number nobody remembers.
If the garage is an L, or there is a bump-out for a workbench or a stairwell, break it into rectangles, work each one out and add them together. Round up rather than down. A quote built on a floor slightly larger than the real one does not surprise anybody later.
What to write down besides the number
How many doors and how wide. Whether there is a floor drain and where. Whether there is a step down from the house, an apron outside the door, or a landing at the side entrance, and whether you want those coated too.
Then whatever is not flat concrete. Cracks, an area that has flaked, an old patch, a stain that has soaked in rather than sitting on top, and anything already on the floor: paint, a sealer, an old coating, or a mastic left from tile.
What the number is for
Square footage gets you a range and tells you whether this is in your budget. It does not get you a quote, because prep is the line that moves and prep is decided by what is on the floor and what the slab reads.
So the measurement plus four photographs is the useful thing to send. It is enough to tell you whether to keep going, and enough for whoever comes out to arrive knowing what they are looking at.