A BMI chart takes your height and weight, and shows you whether you are overweight, underweight or about right. It's not completely perfect (for instance if you've been spending a long time pumping iron in the gym then you might be heavy but not actually overweight) but it's a pretty good guide.
At Swim Smooth we have a similar chart that gives you insight into your swimming. We call it the Stroke Rate Chart and it looks like this:
This has two axes, your swimming speed (time per 100m) and your stroke rate (the number of strokes per minute you take counting both arms).
The chart has three zones:
The Red Zone indicates your stroke rate is too high for your swimming speed. If you are in this zone, there's a strong likelihood you are fighting the water - a low body position, crossovers and scissor kicks are common.
With a Pro subscription, use the Swim Smooth Guru to follow either the Arnie or Swinger processes and tune up these elements of your stroke. You'll move into the white zone and immediately notice the difference in your swimming:
The Blue Zone indicates your stroke rate is too low for your swimming speed. If you are in this zone it's likely you have a pause and glide in your stroke timing which is holding you back. You are also likely to be dropping the wrist and pushing forwards on the water - we call this "putting on the brakes" and it's fundamentally connected to over-gliding.
With a Pro subscription, use the Swim Smooth Guru to follow the Bambino or Overglider processes and you'll soon be swimming much more effectively:
The White Zone is where you should be. That's not to say that your stroke is perfect but it says that your stroke rate is about where it should be and not something to be concerned with.
The width of the white zone takes account of two things:
2) Your individual stroke style. For instance if you have an effective 6 beat kick and like to use it then your stroke will be longer with a slightly slower turn-over for a given speed.
If you are in the red or blue zones, then you now have some direction to improve the effectiveness of your individual swimming.
You can find out more about the Stroke Rate Chart here together with non-elite and elite swimmer examples: