All our sizes are given in an easy to understand ( we hope), format. Europe is different to the UK, is different to the USA / Canada, is different to Asia, Australia, New Zealand, the Pacific Islands and South America.
Then you have mattress manufacturers. Many are still using hand measurements and many are computer sized. Neither is perfect.
The sizes below are generally rounded down to the nearest 10 mm or 1/2 inch. Manufacturers discrepancies usually come in at 3 – 5mm ( ¼” ).
So if your measurement is plus or minus 10mm or 1/2 inch of the dimensions given on the product, there should not be a problem.
( Yes I know, 30cm / 11 ¹³/₁₆” does not = 1 foot! and 25 cm / 9 27/32 does not = 10″ but these are the tolerances we are working with ).
For the most part we have rounded down.
If your measurements are within ½ an inch or 10mm (either way), of these, then chances are you will get a perfect fit with your bedding or other selection.
While we love our postal services we don’t believe in paying them more than we need to, and they probably don’t want to be increasing their work load by returning and resending packages.
If we can get it right first time then it is win / win.