Before you buy it, find out whether it fits, and whether it can even get in.

Every furniture preview app answers whether it looks good in the room. None of them tells you no. Elbow Room answers the question that actually costs money and plaster: can the thing get through the door, along the hall, and around the turn.

I bought a couch that would not go down my basement stairs. The flight turns ninety degrees on three winder treads, with no landing and nowhere to stand it up and swing it. I found out halfway, with the couch wedged and the wall already gouged.

Then it happened again to somebody else, with a water heater, on the same stairs. Nobody measured it either time, and there was nowhere to look it up.

Point your phone at a space, then ask it about something you are thinking of buying.

• Can it get there: doorways, halls, stairs and winder turns
• Can it be there: floor area, headroom, height limits and setbacks
• Real product dimensions, looked up and cited rather than guessed