Help please with marks and spencer sizing

[devilsavacado]

Just looking at the M&S website to order some schoolwear in their sale and am confused as to the sizing.

The sizing guide says 4-5 yrs or 5-6 yrs,but when you come to order it just says as an option 5 or 6.

I need 117cm so 5-6 yrs so do I order 5 or 6?

Can anyone advise please?

Have just found it.[blush}