Arched doors are unforgiving. Unlike rectangular openings where a few millimetres of tolerance is absorbed by the frame, arches need to be measured to the millimetre and — for anything with real curvature — templated physically. Here's how we do it, and what to check if you're taking preliminary measurements yourself.
Measure horizontally at the widest part of the opening (usually just above the springline where the arch begins). Use a rigid tape, not a soft measure. Record to the nearest millimetre.
Take this measurement at three points: near the springline, mid-height and near the sill. If the numbers differ by more than 3mm, the frame is not square and this needs to be noted.
From the finished floor level to the highest point of the arch (the crown). Take three vertical measurements: on the centreline of the opening, and 100mm in from each side.
The centreline is the critical figure for arched-door manufacture. The side figures tell us whether the frame's arch is symmetrical.
Arches come in named profiles: round-top (semicircle), segmental (partial circle, less than 180°), gothic (pointed), ogee (S-curve), Tudor (four-centre pointed). Take a clear photograph of the opening from directly in front, and — critically — measure the height of the springline (where the arch begins) from the finished floor.
For anything that isn't obviously a simple round-top, we need a physical template. Photographs alone don't capture arch geometry accurately enough.
For anything more complex than a round-top arch on a small opening, a paper or hardboard template of the arch is the only reliable way to capture the exact geometry. Tape hardboard against the frame, mark the arch outline with a pencil transferred through, and cut carefully.
If you're not confident doing this — most people aren't, for good reason — book a survey visit. Our teams template as standard on every arched-door survey nationwide.
Look at the frame's condition, squareness and material. Is it timber, masonry-set or metal? Are there mouldings that need to be worked around? Is the sill level, or dropping? All of this affects manufacturing tolerance and fit.
The most common errors we see on customer-provided measurements: (1) measuring only one horizontal point, missing frame twist; (2) not identifying the springline height, so we can't infer arch geometry; (3) taking measurements over existing beading rather than to the finished frame; (4) not accounting for finished floor level if a new floor is planned.
None of these are fatal — but they're why we always survey and template on-site before manufacturing anything curved.
Preliminary measurements from you help us give an accurate initial quote, but for arched doors we survey and template on-site before manufacture in almost every case. That's not upselling — it's why our doors fit cleanly on installation day.
