The abbreviation IPPT stands for (Inch-lbs.-per-turn). Every torsion spring has an IPPT number and the purpose is to have the right IPPT for the weight of your door. Sometimes one single spring will have enough IPPT of two smaller springs each with half the IPPT of the single spring. And to calculate this formula you will need more than just the weight of the garage door the weight of the garage door is just a part of the equation. You will need three things: the door weight, high moment arm and the number of turns to balance the garage door. To determine the number of turns to balance your door you just have to know the height of the garage door for example a 7-foot high garage door torsion spring will need 7 full turns to balance that garage door in other words it’s one full turn per foot of height of the door.
measurement from the center
And the moment arm is usually the measurement from the center of the cable drum to the outer edge of the cable drum and on an average 7 foot high garage door that would be to 2 inches. So here is a simple formula you can use.
(Door Weight X Hi moment arm / Divided by # of turns = IPPT) so your IPPT should equal about half of the doors weight if your garage door requires 2 springs then you would have to add the IPPT of both springs and that should equal half of the weight of the garage door. Or if you are using just one torsion spring then the IPPT of the single spring should equal the weight of the garage door.