sand cement screed

We have had an extension and wet UFH installed across the whole ground floor (new and old). UFH in the new extension is clipped on top of celotex. UFH in the existing is embedded in an insulation board. - about 45m2 in total We've had a floating screed installed (Longfloor CT-25/F5) and 3...

Just wondering if you knowledgeable folk could tell me if I have this correct. 26M² of screed needed at 75mm depth, sitting on 100mm kingspan. Looking at 4:1 mix. After trawling around trying to find a calculator (can't find the one that used to be a sticky) I have come up with the following...