This is a nice chart to help choose what band will fit your needs best. I also threw the data into Excel to get a graph.
Also, here is a note from Thera-Band:
Using the “force elongation” chart, you can predict what the force will be at a specific percent elongation for Thera-Band colors. For example, if your 2 foot length of band was Red, then when you stretched it to 4 feet (100% elongation), you’d have about 3.9 pounds of force.
Both Thera-Band resistance tubing and bands are calibrated to offer the same resistance levels at the same percent elongation.