Common bay window measurement mistakes
Most avoidable problems come from a change of reference line, a missing clearance or an assumption about a product.
Mixing units
A measurement of 120 cm is 1,200 mm. Write units next to every number. Changing the calculator’s unit converts valid dimensions rather than changing their physical size. Unusually small or large dimensions are flagged so you can check them.
Measuring the frame and ordering a track
A track projected away from the frame follows a different path at a corner. Mark whether you measured at the frame, a proposed track line or an existing system. The calculator does not guess an offset or automatically add a standard allowance.
Treating the total as an order length
A sum of straight sections is a useful reference, but bend geometry, end returns and joints remain unresolved. Do not round up to a retail pack size until the supplier confirms the required finished length and whether joining is permitted.
Missing blind corner clashes
Blind headrails and controls need space at the corners. Use the supplier’s depth figures for the selected blind and mounting type. Do not subtract a generic clearance from every bay.
Measuring curtain fabric too early
Your desired drop helps planning, but final curtain dimensions depend on the fitted system and heading. Confirm the supplier’s measuring points after the track or pole position is agreed.
Sources & further reading
- B&Q: measuring a bay window
- English Blinds: angled bay measuring method
- Dunelm: bay window measuring guide
Reviewed 2 November 2026. Check the current instructions for your chosen product.
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