Spring Count & Size by Door Weight
Find the load each spring must carry from your door’s weight and how many springs it runs, so a technician can pick a spring rated at or above that load.
Calculator
A 291 lb door on 2 springs puts about 146 lb on each — pick a spring rated at or above that load from a labeled wind/IPPT chart. A balanced pair is standard on wide doubles. ⚠️ These are labeled planning typicals; the exact wire size, inside diameter and length must be set by a trained technician.
A torsion spring has to counterbalance the weight of the door, so the first thing a good technician establishes is how much the door weighs and how that weight is split across the springs. This helper does the split for you: it divides the door weight by the number of springs to show the load each one must hold, which is the starting point for choosing the correct wire size, inside diameter and length.
Most wide or heavy doors run a balanced pair so no single spring is overloaded and the door stays even if one ever fails. A light, narrow single door may use one spring. This tool tells you the per-spring load; the exact spring specification is then read off a labeled wind/IPPT chart by the technician.
Formula
The load each spring carries is the door weight shared equally between the springs:
load_per_spring = door_weight_lb ÷ spring_count
Pick a spring rated at or above that load. A balanced pair halves the load on each spring compared with a single-spring setup, which is why doubling up is standard on heavy doubles.
Worked example
A typical 16 × 7 ft two-layer steel door weighs about 291 lb. On a balanced pair:
- Load per spring: 291 ÷ 2 = ~146 lb
So each of the two springs must be rated to hold roughly 146 lb of door. If the same door ran a single spring, that one spring would carry the full 291 lb — a much larger, more heavily-stressed spring. Feed the door weight from the weight estimator if you do not have a spec sheet.
From load to the actual spring
The per-spring load is only the starting point. The actual spring is defined by three things a technician measures — wire diameter, inside diameter and wound length — matched to the door’s height (the drum size and cable drop). Two doors of the same weight can need different springs if their travel differs. Never assume a spring is correct just because its rated load matches; the full specification must come from a labeled chart and the door’s geometry.
Because this is a labeled planning typical and because springs store extreme energy, use the number to discuss the right spring with a trained technician, not to buy and wind a spring yourself. Pair it with the cycle-life helper to also choose a rating that suits your daily use.
Reference table
Load per spring across common door weights on 2 springs:
| Door weight | Load per spring |
|---|---|
| 150 lb | 75 lb |
| 200 lb | 100 lb |
| 250 lb | 125 lb |
| 291 lb | 146 lb |
| 350 lb | 175 lb |
| 450 lb | 225 lb |