It all depends on the strength of the Ibuprofen that you have. But a good way to calculate is take whatever the recomended dose is and divide by the (100/your baby's weight)
ex. If your baby is ten pounds and it says to give 5mg give your baby 1/2 a mg.
ex. If your baby is ten pounds and it says to give 5mg give your baby 1/2 a mg.