I measure it in all sorts of ways now really. I used to go by the scale and BMI. Now I use periodic fitness assessments with Jodi at the gym. I’ve talked about them before. Basically I’m at a point now where the scale is just habit and not really necessary.
I use skin folds, muscle and body fat percentage measurements to keep tabs on how I’m doing. I also keep track of times for running and biking which lets me know how I’m doing really. Am I slower, am I faster.
I also have my workout charts at the gym, I just use them to track how much I am lifting when I raised the amount and such. So once I got over the scale I use way more tools to measure my fitness, but they are more about ability than anything.