We have site tested this garage door weight calculator out in the field while also comparing it to our suppliers stock door weights.  After extensive testing, we found that the calculator in question repeatedly over weighed every door by 10-30%. 
To prevent injury, we recommend that you not use this calculator to estimate your door weight.  We rely on our own scale, or bathroom scale in the field. 

Weigh the door. We recommend weighing the door to confirm the torsion spring dimensions. Provide also the door height and track radius of 12" or 15".

To weigh the door place a bathroom scale under the center of the door if it is a single-car door. A short piece of flat wood scrap will help protect the door and provide more accuracy by evenly distributing the weight on the scale. (Do not use digital scales.)  Two scales are sometimes necessary for larger, heavier doors.  Just place one scale one each side of the garage door, about 18" from end.  Add the two measurements together for door weight. 

This is a tried and true method that works.  Please call us if you have any questions.  1-800-997-7606