Piglet John et al How do I measure the radius of a quadrant shower tray pls?

[Celeriacacaca]

We're replacing out shower surround but need to keep the shower tray which is a quadrant tray. The bathroom shop couldn't advise how to calculate the radius of the tray so we can check if a new surround will fit. Can anyone tell me how please?

Draw a sketch of it from above
Measure from the right angle corner to the furthest point from the corner
Mark the distance on the sketch.
Take it to the shop and let them deal with it

Just a point, we got into problems with our quadrant shower tray. I thought they were all the same. I had chosen a surround but just asked the builders to get any tray that had the drain in the right place.

Turns out the flat "shoulder" around the edge (the glass sits on it) is the same outside radius but is narrower than the one the surround was designed for, consequently our door doesn't quite shut at the bottom. Of course this became apparent only after it was all tiled and plumbed in. And because I'd bought all the stuff myself I couldn't blame the builder!

The enclosure will have a couple of centimetres of adjustment but try and find the dimensions of the one you are interested in and check the tray from its own range against your tray. The trays are not exactly a quarter circle, they tend to have a straight bit each side then a 550mm radius. The shoulder can be 50 - 80 mm wide.