Garage door lift cables: how to pick the right size and length

Lift cables carry the whole door. A cable that's too light frays early, and one that's too short won't reach the bottom bracket with wraps left on the drum. Two numbers decide both: the door's weight and its height.

Cable diameter by door weight

Most residential and light commercial doors use 7x7 galvanized aircraft cable. DoorBot's cable sizing tool uses these steps:

• Up to 150 lb: 1/8" cable, about 2,000 lb breaking strength.
• 151 to 300 lb: 5/32" cable, about 2,800 lb.
• 301 to 500 lb: 3/16" cable, about 3,700 lb.
• Over 500 lb: 1/4" cable, about 6,100 lb.

Don't know the weight? Estimate it from the size and construction with the door weight estimator, or check our door weight chart.

Check the safety factor

The tool also shows a safety factor: the cable's breaking strength divided by the door's weight. A 140 lb door on 1/8" cable has a factor of about 14. That margin matters. Cables wear where they wrap the drum and where they meet the bottom bracket, and a door that binds can shock-load them.

When a door sits near the top of a weight range, going up one cable size costs little and buys a lot of margin. Make sure the drums are grooved for the cable you choose.

Cable length

• Standard lift: door height plus 18 inches. A 7-foot (84") door takes about 102" of cable per side.
• Vertical lift: twice the door height plus 18 inches.
• High lift: door height, plus the high-lift distance, plus 18 inches.

The 18 inches covers the wraps that stay on the drum and the loop at the bottom bracket. Cut long rather than short: extra cable can be trimmed at the drum, but a short cable means a second trip. The cable drum reference shows which drum goes with which lift.

When to replace cables

• Frayed strands, rust or kinks anywhere along the cable.
• A cable that came off the drum and was wound back on under load.
• Any spring replacement on a door whose cables are more than a few years old. Replace both sides together so they wear evenly.

Safety: the bottom bracket is under spring tension through the cable. Never loosen it with the springs wound. Unwind the springs first, then work on the cables. The cable replacement procedure walks through it step by step.

Field rule: weight picks the diameter, height and lift pick the length, and both cables get replaced together.