To get from metric U-value to American R-value:

Multiply the U-value by 0.176. At this point, the units will remain the same, Watts per Kelvin meters squared. For example, begin with a U-value of 0.247 Watts per Kelvin meters squared. Multiplying through gives you (0.176)*(0.247) = 0.043472 Watts per Kelvin meters squared.

Divide 1 by 0.043472 which gives you (1/0.043472) = 23.0 American R-value.