Garage door weight and spring sizing

Disconnect the opener with the emergency release cord. Lift the door by hand to roughly waist height and let go.

A correctly sized spring holds it there. If the door falls, the springs are undersized or have lost tension. If it rises on its own, they are oversized or overwound.

Either error means the opener is fighting the difference on every cycle. An opener is designed to guide a balanced door, not to lift an unbalanced one, and this is the single most common reason an opener fails years before it should.

Insulation. Polyurethane-injected sections are significantly heavier than single-skin steel, which is why fitting an insulated door and reusing the old springs is a specific and serious mistake.

Glazing. Window sections add weight unevenly, concentrated in whichever row carries them.

Material. Wood and wood-composite doors are considerably heavier than steel of the same size, and their weight changes seasonally as they absorb and release moisture.

Age. An old wooden door that has taken on water can weigh meaningfully more than it did when the springs were fitted, which is why balance drifts on older doors without anything obviously breaking.

Two doors of identical width and height can need entirely different springs. Size determines the geometry of the system; weight determines the spring.

This is what a cheap spring quote is usually cutting. Fitting a stock spring that is approximately right is faster and cheaper than measuring the door and ordering the correct one, and the door will appear to work on the day.

The consequences show up over the following months as an unbalanced door, accelerated opener wear, and a spring that reaches its fatigue limit early.