Garage door cable length calculator
What length lift cables does the door need? Enter the door height (and any high-lift) to get the cable length to order, plus the cable diameter for the door weight.
Torsion (standard or high-lift). Extension-spring cables route over pulleys and are sized differently. Always replace cables in pairs.
The cable-length rule
A lift cable has to reach from the bottom bracket all the way up to the drum, plus enough to wrap the drum with the door fully open. That extra is why the field rule is:
Cable length = door height + 18".
It matches how cables are sold, which is a good sanity check:
| Door height | Cable length |
|---|---|
7 ft | 8' 6" (102") |
8 ft | 9' 6" (114") |
10 ft | 11' 6" (138") |
12 ft | 13' 6" (162") |
14 ft | 15' 6" (186") |
Running high-lift? Add the high-lift rise on top — the cable has to cover the extra vertical travel.
Cable diameter by door weight
The two cables split the door's weight, and the trade sizes them to roughly a 5:1 safety factor (ANSI/DASMA 102). Bigger, heavier doors step up:
| Door weight | Cable | Typical use |
|---|---|---|
Up to 400 lb | 1/8" | 7x7 or 7x19 galvanized aircraft cable — the residential standard. |
400–700 lb | 5/32" | Heavier residential and light-commercial doors. |
Over 700 lb | 3/16" or larger | Commercial and heavy doors — confirm the spec with the door maker. |
Extension springs are different
This calculator is for torsion cables running to a drum. On an extension-spring door the lift cable routes from the bottom bracket, over a pulley, back to the rear track hanger — so its length depends on the pulley layout and track, not the door-height-plus-18 rule. Use the door manufacturer's spec there, and don't forget the safety cables through the springs.
Frequently asked questions
What length cable does a 7-foot garage door need?
About 8 feet 6 inches (102 inches). The field rule for standard-lift torsion is door height + 18 inches — the extra covers the wraps on the drum and the bottom-bracket attachment. That is also how cables are sold: 8'6" for a 7-ft door, 9'6" for an 8-ft door, 11'6" for a 10-ft door.
How do I measure garage door cable length?
You size it from the door height rather than measuring the old cable, which may be stretched or the wrong part. Take the door opening height, add 18 inches, and add any high-lift rise. Replace cables in pairs.
What diameter garage door cable do I need?
Most residential doors use 1/8" 7x7 or 7x19 galvanized aircraft cable. Heavier doors move to 5/32", and commercial doors to 3/16" or larger. Each of the two cables carries about half the door, and the trade sizes to roughly a 5:1 safety factor.
Do extension springs use the same cables?
No. Extension-spring lift cables route from the bottom bracket over pulleys to the rear track hanger, so their length depends on the pulley layout, not the simple door height + 18" rule. Use the door manufacturer's spec for those.
Audrey does this in the truck — hands-free.
This calculator runs the exact logic built into Ask Audrey, where your techs just ask out loud and get the answer cited to your own manuals — plus spring specs, winding turns, and door weight. Every tech, a senior tech.