I just need to know if my calculations are right or

All on my Gpz1100
I'm changeing the rear end with an 18" wheel.The circumference of the original wheel is 2,092mm and the circumference of the new wheel is 1,885mm(incl tyres). The original rear wheel sprocket is 42teeth so that is approx; 50mm of circumference per tooth. So therefore (I think) I need a new sprocket of 38 teeth calculated by 1885 divided by 50 =38
Is that right

Then convert this and the front sprocket size to 530 type by using something like jtsprockets

Any help would be appreciated

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Chris