IPPT (Inch-Pounds Per Turn)

IPPT (inch-pounds per turn) is the standard industry unit for describing a torsion spring's torque output. Every torsion spring has a fixed IPPT rating determined by three physical properties: the wire diameter, the coil inside diameter, and the spring material. A spring with a higher IPPT delivers more torque per revolution of winding and is, in practical terms, a stiffer spring.

How technicians use IPPT to size a spring:

1. Measure the door weight (in pounds) using a scale or estimated from the door's specifications.
2. Determine the cable drum radius (in inches). Most residential drums have a 2-inch radius, meaning one full drum rotation lifts the cable 2 x pi x 2 = about 12.6 inches.
3. Calculate turns required to raise the door from closed to fully open: door height divided by rise per turn. For a 7-foot door on a 2-inch drum, this is roughly 84 / 12.6 = about 6.7 turns.
4. Required total torque = door weight x cable drum radius = for a 200-pound door, 200 x 2 = 400 inch-pounds.
5. Required IPPT = total torque / turns required = 400 / 6.7 = about 60 IPPT.

So a spring rated at 60 IPPT, wound 6.7 turns, will deliver 400 inch-pounds of torque to offset a 200-pound door.

IPPT is set by the spring's physical geometry and cannot be changed in the field. If a spring has too low an IPPT for the door weight, the only fix is to replace it with a stiffer spring (larger wire diameter, smaller coil diameter, or both). Using a spring with too high an IPPT and winding it fewer turns leaves the spring under-stressed and prone to inconsistent performance.

For example, a Service Spring catalog might list a 0.225-inch wire diameter, 1-3/4-inch inside diameter spring at 62 IPPT. A tech looking to balance a 195-pound door with a standard drum would confirm that 62 IPPT x 6.5 turns = about 403 inch-pounds, close enough to a correct match.

IPPT interacts closely with spring cycle life: winding a spring to a higher fraction of its rated capacity reduces cycle life, while a correctly sized spring at its design stress lives the full rated cycle count.

Want to put numbers to this? Use the interactive torsion spring winding and ippt estimator below, or open the full torsion spring winding and ippt estimator with examples and notes.