What Garage Door Spring Size Do You Need?

A garage door that suddenly feels far too heavy, will not stay open, or slams shut is often telling you the spring system has failed. Before ordering a replacement, the question is not simply what garage door spring size looks about right. The correct spring must match the door’s weight, lifting arrangement and fittings. A near match can leave the door unsafe, difficult to operate and capable of damaging cables, rollers or an electric opener.

For UK garage doors, spring identification can be straightforward when the original part is intact and marked. It becomes less certain when a spring has snapped, the door is older, or previous repairs have mixed parts from different manufacturers. This guide explains what to measure, what not to guess, and when a complete manufacturer-specific spring assembly is the sensible option.

What garage door spring size means in practice

Spring size is not one measurement. A garage door spring is specified by a combination of dimensions and performance requirements. The key aim is to counterbalance the door, so it can be lifted by hand with reasonable effort and held reliably in the open position.

For a torsion spring, the usual specification includes wire diameter, inside diameter, overall body length, wind direction and the number of turns or torque required. Cycle rating also matters. A standard spring may be designed for a limited number of opening and closing cycles, while a higher-cycle alternative can be worthwhile for a frequently used garage or a shared access door.

Extension springs are specified differently. Their closed or free length, outside diameter, wire size, end fittings and pull rating all affect suitability. On an up-and-over door, the spring also has to work with the existing cables, pulleys, brackets and lifting arms. This is why an apparently similar spring is not necessarily interchangeable.

The door type is just as relevant as the spring itself. Canopy up-and-over doors, retractable up-and-over doors, sectional doors, roller garage doors and side-hinged doors use very different counterbalance arrangements. Some older Cardale, Garador, Henderson, Hormann, Novoferm and Gliderol doors use distinctive spring units or fittings that should be matched by application rather than dimensions alone.

Identify the spring system before measuring

Start by looking at where the springs sit when the door is closed. Torsion springs are usually mounted on a shaft above the opening, often behind a cover or within a barrel. Extension springs normally run along the sides of the door, above the horizontal tracks, or form part of a side-mounted lifting assembly.

An up-and-over door may have one or two side springs, sometimes concealed within a mechanism. A roller garage door may use a spring inside the curtain barrel, but electrically operated roller doors can also have issues related to the motor, limits or curtain alignment rather than the spring. Do not order a spring simply because the door feels heavy until the rest of the mechanism has been checked.

Look for a label, part number, stamped marking or manufacturer reference on the spring, cone, shaft, lifting arm or door panel. This is often the quickest route to the right replacement. Take clear photographs of the complete mechanism, not only the broken component. The position of the hooks, cones, pulleys and brackets can identify a part that measurements alone cannot.

Check whether the spring has actually failed

A visible gap in a torsion spring is a clear sign of breakage. With extension springs, look for a snapped coil, stretched-out body, distorted hook or detached fitting. However, a door can also lose balance because a cable has slipped from a drum, a pulley has seized, a roller has failed, or a lifting arm is bent.

If one spring in a paired system has broken, the other may be close to the end of its service life. Replacing both matched springs is often better value than fitting one new spring beside one fatigued component. It helps maintain even lifting force and avoids a second repair shortly afterwards.

How to measure a torsion garage door spring

Torsion springs are under substantial tension when fitted. Do not loosen winding cones, remove cables or attempt to unwind the spring to take measurements unless you are trained and have the correct winding bars. Screwdrivers, grips and improvised bars are not safe substitutes.

Where possible, measure a detached, fully relaxed spring or use information from the original specification. You need the wire diameter, inside diameter, body length and wind direction.

Wire diameter is best measured across 20 consecutive coils with a vernier calliper or steel rule, then divided by 20. Measuring a single coil can introduce enough error to produce the wrong result. Count complete coils only and measure in a straight section away from the cones.

Inside diameter is usually stamped on the winding or stationary cone. If it is not marked, measure the internal width of the spring body, not the outside. Measure the body length from coil to coil, excluding cones. Finally, establish the wind direction. A right-wound and left-wound spring are not interchangeable, even if every other measurement matches.

Do not assume that a longer spring is stronger. Spring lift is determined by the relationship between wire diameter, coil diameter, length and the number of active coils. Two springs can look similar but deliver very different torque.

Why door weight and hardware still matter

A correctly sized torsion spring is selected around the actual door weight and drum arrangement. Added timber cladding, insulation boards, replacement glazing or waterlogged panels can make an older door heavier than its original specification. Conversely, a lightweight replacement panel may alter the balance in the other direction.

A properly balanced manual door should lift smoothly and stay roughly in place at about halfway open. This is a useful performance check, but it is not a safe method for choosing spring size while a broken or disconnected spring system is in place. If the door is heavy or unstable, keep people, vehicles and belongings clear of its path.

Measuring extension springs and up-and-over door springs

For an extension spring, record its relaxed overall length, body diameter, wire diameter and the end style. The end may be a hook, loop, threaded fitting or a manufacturer-specific attachment. Measure the spring only when it is not under tension.

Also note where it mounts: the fixed bracket position, cable route, pulley arrangement and connection point at the door mechanism. On retractable up-and-over doors, a spring can be one part of a wider cable and lever system. Replacing it with a generic spring that has the wrong hook length or pull force can cause uneven lifting or prevent the door from closing properly.

For older doors, the most reliable approach is often to identify the manufacturer, door model where known, door width and height, and the arrangement of the existing hardware. A complete matched spring kit may include the correct cones, cables or fixing brackets, removing uncertainty created by worn or altered original parts.

Avoid these common sizing mistakes

The most costly mistake is ordering by appearance. Spring finish, colour coding and the number of coils are not enough to confirm a specification. Colours can vary between manufacturers, and a spring that fits physically may still be wrong for the door.

Another common error is using the opening size instead of the actual door type and weight. Two doors of identical width and height can have very different panel construction, glazing, insulation and lifting gear. The spring is selected for the moving door and its hardware, not the brickwork opening.

It is also unwise to compensate for a weak spring by adjusting an electric opener. An opener is designed to move a balanced door, not lift its full weight. Continuing to use automation on an unbalanced door can overload the motor, strip drive components or create a trapping risk.

Finally, do not reuse damaged cables, cracked cones, worn pulleys or badly corroded brackets simply because the spring is new. These parts work as a system. If a cable has frayed or a pulley does not rotate freely, replace the affected component at the same time.

When to use manufacturer-specific spares

A measured generic spring can be appropriate for a standard, clearly identified torsion arrangement. Manufacturer-specific parts are usually the better choice when the door uses proprietary side mechanisms, unusual cones, integrated cables or older hardware where compatibility is uncertain.

Have the manufacturer name, door style, approximate age, door dimensions, part markings and photographs ready before ordering. For a snapped spring, photographs of both sides of the mechanism are particularly useful. Northwest Garage Door Spares can help narrow down compatible spring, cable, cone and hardware options when the original reference is unclear.

If the spring is fitted under tension, the shaft or brackets are damaged, or the door is large and heavy, arrange a competent garage door engineer to carry out the repair. The cost of professional fitting is small compared with the risk of injury or damage caused by a released spring or falling door.

The right replacement should leave the door smooth, balanced and secure, not merely moving again. Take the time to identify the complete lifting system before buying, and you will be far more likely to restore dependable operation for years rather than create the next fault in a few weeks.