@fileunderwater's suggestion to use a scale is probably the best answer you could get, but looking at this broadly, the answer is no. The oft-referenced apple and pear shapes are indeed very real and have medical consequences. One of the issues is that there are sex differences in fat distribution. There is no evidence I can find that finger fat is a good correlate of overall body fat, although admittedly yours could be. It is also likely a function of how much overweight you were when you began the "experiment" i.e. the relationship probably isn't linear.
That being said, in men the ratio of the _length_ of the second and fourth digits are otherwise meaningful.