A single photo can give you real sizes if it contains something of known height and the camera isn't playing tricks. This is what Fits Here needs, and what makes any photo better for planning.
- Use the 1x lens. Ultra-wide (0.5x) and Pano bend straight walls, and bent walls can't be measured.
- Stand in a corner at chest height and hold the phone level. Photos from high up or near the floor exaggerate depth.
- Get a door in the shot, top and bottom. US interior doors are 80 in tall, which sets the scale.
- Show where the wall you care about meets the floor, both ends if you can.
- If you have a tape measure, measure that wall. With one real length, every number becomes exact instead of approximate.
Why one wall and one door are enough
The floor is a flat plane. Two taps where a wall meets the floor give its direction, and a door of known height tells us how high the camera was. From there every floor point has a real position, in inches.