Garage Door Torsion Spring Calculator
Replacing a torsion spring starts with knowing exactly what's on the shaft. Measure the broken spring's wire size, inside diameter, and length, weigh the door, and this calculator computes the spring's torque rating (IPPT), the winding turns your door needs, and whether the spring was sized right in the first place.
One thing up front: springs are wound under extreme tension, and winding them injures DIYers every year. Use this tool to know what you have — then hand the install to a tech with winding bars.
How this works
The spring's torque rating uses the standard torsion spring formula: IPPT = (E × d⁴) ÷ (10.8 × D × N), where E is 28,500,000 psi (Young's modulus for music wire), d is the wire diameter, D is the mean diameter (inside diameter + wire size), and N is the number of active coils (spring length ÷ wire size). IPPT — inch-pounds per turn — is how much torque the spring delivers for each full turn it's wound. Wire size is measured the way spring techs do it: the length of 10 coils divided by 10, cross-checked against 20 coils, which beats calipers on a rusty spring. DASMA TDS-171's color-code chart is the other cross-check — wire sizes map to standard paint colors on the coil end.
The demand side comes from the door: a door balanced on standard 4-inch drums needs torque equal to its weight times the 2-inch drum radius. Winding turns follow DDM's published method — door height in inches divided by the drum circumference (12.57 inches of cable per turn), plus one turn to keep cable tension — about 7.7 turns for a 7-ft door and 8.6 for an 8-ft door. Dividing required torque by winding turns gives the IPPT the door demands; a spring supplying 90–110% of that is considered correctly sized, which is why the accuracy of the door weight matters more than anything else you enter (weigh it — don't estimate).
And the part we won't soft-pedal: this calculator deliberately stops at identification. Winding a torsion spring stores hundreds of pounds of force in a steel coil inches from your face, and it sends DIYers to the ER every year. Garage Door Repair Network is a referral service, not a contractor — we route your request to independent local techs who carry the right spring (or a high-cycle equivalent with the same IPPT) and wind it with proper bars. Formulas and constants are checked annually against DDM's methodology and DASMA technical data sheets.
Estimates only — independent local providers quote their own pricing. Data last reviewed 2026-07.
Frequently Asked Questions
How do I measure my garage door torsion spring?
Three measurements: wire size (measure 10 coils end-to-end and divide by 10 — e.g. 2.25" across 10 coils = 0.225" wire), inside diameter (usually stamped on the cone: P200 = 2"), and overall coil length measured unwound, cone to cone. On a broken spring, measure both pieces of the coil and add them together. Measure with the spring unwound only — never touch a wound spring.
What does IPPT mean on a torsion spring?
Inch-pounds per turn — the torque the spring delivers for each full turn it's wound. Multiply IPPT by the winding turns (about 7.7 for a 7-ft door on 4" drums) and you get the total lift torque. A correctly sized spring supplies within 90–110% of the door's requirement: door weight × 2" drum radius, divided by the turns.
How many turns does a garage door torsion spring need?
Door height in inches divided by the drum circumference, plus one turn for cable tension. On standard 4" residential drums (12.57" circumference), that's about 7.5–7.7 full turns (roughly 31 quarter-turns) for a 7-ft door and about 8.6 turns for an 8-ft door. Techs wind in quarter-turn increments and fine-tune to the door's balance.
Can I replace a garage door torsion spring myself?
We don't recommend it, and this tool is built to stop at identification. Winding a spring stores the door's full lifting force in a coil at head height, and a slipped winding bar causes serious injuries every year. A pro replacement runs $200–$300 for a single spring and $250–$450 for a pair installed — use this calculator so you can sanity-check that the tech installs a correctly rated spring.
Should I get standard or high-cycle springs?
Standard springs are rated ~10,000 open/close cycles; high-cycle springs run 25,000–50,000. A high-cycle spring keeps the same IPPT by using a longer spring with heavier wire, so the door feels identical but the steel is stressed less each cycle. If you open the door 6+ times a day, the upgrade usually pays for itself.
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