The ratio 9:9 is equivalent to 1:1. To find the equivalent ratio, you need to divide both numbers in the ratio by their greatest common factor (GCF). In this case, the GCF of 9 and 9 is 9. Dividing 9 by 9 gives us 1, and dividing 9 by 9 also gives us 1. Therefore, the equivalent ratio is 1:1.