JupiterBlue

Metric size
calculator

Convert between structural opening and panel size, with the right tolerance baked in.

Calculation type

Width (mm)

Height (mm)

Result

— × —

Standard 5mm fitting tolerance applied

Why the 5mm difference?

For a smooth fit, we recommend a 5mm tolerance around the panel. So if your structural opening is 600×600mm, you'll order a 595×595mm panel — leaving 2.5mm clearance on each side for the frame and a clean install.

Tips for measuring

Always measure the structural opening at the narrowest point — both width and height.
For ceiling installations, check that the opening is square. Old joists move over time.
If you're cutting a new opening, mark the panel size on the substrate first and add 5mm all round before cutting.
Beaded frames need a clean opening edge — they sit flush and get plastered in.

Jupiter Blue Proof, not promises Est. 2007

Parcels dispatched since 2007

1.1M+

Customer rating

4.85/5 · 2,246

UK postcodes served

63,251

Next Day Delivery success rate

97.9%

Products in range

128

Fire Rated

Independently fire-tested

Certified Fire Rating: Independently tested and certified to BS 476: Part 22, providing 60 minutes of Integrity and Insulation in both wall and ceiling applications.

View Access Panels → Certified