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Calculation Machine

Garage Door Torsion Spring Calculator

Wire size, IPPT and turns for a replacement spring.

Reviewed by the Calculation Machine team · How we check our maths

Your values

4in drum = 2in radius

ⓘ Live results

Results
Winding turns
6.68
Total IPPT needed
44.9
IPPT per spring
44.9
Lift capacity check
150 lb
Safety
Wind springs with two proper winding bars only — never screwdrivers

Quick answer

Required IPPT = door weight × drum radius ÷ number of turns; a 7 ft door on 4-inch drums normally needs 7.5 winding turns.

The formula

IPPT = weight × drum radius ÷ turns

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Door weight150 lb
  • Door height7 ft
  • Drum radius2 in
  • Number of springsSingle spring

Result

  • Winding turns6.68
  • Total IPPT needed44.9
  • IPPT per spring44.9
  • Lift capacity check150 lb
  • SafetyWind springs with two proper winding bars only — never screwdrivers

How to use the Garage Door Torsion Spring Calculator

  1. 1Weigh the door on a bathroom scale with the springs disconnected.
  2. 2Enter the door height and drum radius.
  3. 3Choose one spring or a matched pair.
Drum radius(in)
4in drum = 2in radius

Frequently asked questions

How many turns does a 7 ft garage door spring need?

About 7.5 turns on standard 400-8 drums — one quarter turn per foot of height plus 7.

Can I replace a torsion spring myself?

Only with proper winding bars and a locked door; a loaded spring stores enough energy to cause serious injury.

About this calculator