How this calculator works
A sofa gets through a doorway in one of two ways. Upright, it passes if its depth and height each fit within the door opening, no matter how long it is, because the length runs along the direction of travel. If it is too tall or too deep to pass upright, it can be turned on its side, and then the limit is the diagonal across the end of the sofa compared with the diagonal of the doorway. Turning a corner in a hallway or on a staircase is a separate constraint: the opening has to be at least as wide as the sofa side, and more space is needed to pivot a long piece.
Formula
sofa end diagonal = sqrt(depth squared + height squared). doorway diagonal = sqrt(width squared + height squared). The sofa passes upright when depth <= door width and height <= door height, and passes tilted when its end diagonal <= the doorway diagonal. Minimum door and hallway width = the smaller of the sofa depth and height.
Worked example
A sofa 220 cm long, 95 cm deep and 85 cm high has an end diagonal of sqrt(0.9025 + 0.7225) = 1.275 m. A 76 cm wide and 200 cm high doorway has a diagonal of sqrt(0.5776 + 4) = 2.141 m, so the sofa passes when tilted even though 95 cm is wider than the 76 cm door. The narrow way through needs a hallway at least 85 cm wide.
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Frequently asked questions
What about removing the door and the legs?
Removing the door gains several centimetres of width and is often the difference between fitting and not. Sofas with removable legs can be many centimetres lower, so measure with the legs off if the height is the issue.
How reliable is the diagonal check?
It is a good first test but it ignores the door frame depth, the skirting board and the space to swing the sofa. Allow some margin; if the numbers are close, measure the actual opening with the door open.
What does a lift measurement change?
An elevator door is often narrower than an apartment door and the car itself limits the turning space. Check the door width and the diagonal of the lift opening before relying on a lift delivery.