How do I measure garage door springs to order the right replacement?

Ordering the wrong spring is one of the most common and costly garage door mistakes a homeowner makes. The wrong wire diameter delivers the wrong torque output, which means the door will not balance properly even if the spring fits on the shaft. Getting the right spring starts with three precise measurements and one visual check. You need calipers or a digital ruler for one of them, but the rest take only a tape measure and about five minutes.

The three measurements you need for a torsion spring

Every torsion spring is specified by three dimensions. All three must match your existing spring or your door weight calculation. Order any one wrong and the door will be unbalanced.

1. Wire diameter. This is the most important measurement and the one where errors hurt most. Even a difference of 0.005 inches in wire diameter changes the spring's torque output noticeably. Do not try to estimate by eye or match to a ruler.

The correct method: use digital calipers (available for $10-$15 at any hardware store) and measure the length of exactly 10 consecutive coils. Write down that measurement in inches, then divide by 10. That gives you the wire diameter. For example, if 10 coils measure 1.75 inches, the wire diameter is 0.175 inches, which is a common residential size.

Common residential wire diameters: 0.162", 0.177", 0.192", 0.207", 0.218", 0.225", and 0.250". If your measurement falls between two common sizes, measure again. Calipers at this price point are accurate to 0.001 inches when used carefully.

2. Inside diameter of the coil. Measure the inside opening of the spring coil, not the outside. Standard residential sizes are 1-3/4 inches (1.75") for most single-car and lighter double-car doors, and 2 inches (2.00") for heavier double-car doors and commercial-grade residential doors. The inside diameter must match the torsion bar diameter, because the spring slides over the bar.

3. Overall spring length. Measure the full relaxed length of the spring in inches, from one end to the other. Standard lengths run from 20 inches to 36 inches in most residential applications. The spring length relates directly to door height and door weight, so an incorrect length means the spring cannot deliver the right number of cycles or the right torque at the right point in the door's travel.

Measurement	Tool	Typical residential range
Wire diameter	Digital calipers (10-coil method)	0.162" to 0.250"
Inside diameter	Tape measure	1-3/4" or 2"
Spring length	Tape measure	20" to 36"

Determining winding direction

Winding direction tells you whether the spring is left-wound or right-wound. This matters because a left-wound spring on the right side (or vice versa) will unwind in the wrong direction and fail immediately.

To determine winding direction: look at one end of the spring straight on. If the wire coming off the end coil points to the right, it is a right-wound spring. If it points to the left, it is left-wound.

Most residential torsion setups with two springs use one of each: the left spring sits on the left side of the center bracket, the right spring on the right side. If you are replacing both springs, you need one left-wound and one right-wound. If you are replacing only one, note which side it is on and match the winding direction.

What DASMA color codes tell you (and what they don't)

DASMA (Door and Access Systems Manufacturers Association) color codes are painted marks on the spring ends that indicate wire diameter. The codes use a two-color system. For example, a spring coded white/white is 0.192", and a spring coded red/red is 0.218". The DASMA guide is available from spring suppliers and widely referenced online.

The color code is a useful starting point, especially if the spring is intact and you can read the paint marks clearly. But it is not a substitute for direct measurement. Two problems: first, there are only about 20 colors in the scheme but more than 20 common wire sizes, so some wire diameters share the same color code with a close neighbor. Second, paint wears off springs after years of use, and cheap offshore springs are sometimes mis-marked at the factory.

Always verify the color code with calipers before ordering. If the marks are worn, measure only. If the marks are fresh and readable, treat them as a double-check on your measurement, not as the sole source of truth.

For extension springs, which run along the side tracks rather than over the door, the DASMA color code system works somewhat differently: the color indicates the weight capacity of the spring, not the wire diameter directly. Extension spring color codes run in 10-pound increments, from tan (100 lbs) up through red (200 lbs) and green (300 lbs). The spring you need should match the weight of your door, which is printed on the door manufacturer's label (usually found on the inside of a door panel) or can be estimated by your garage door technician.

Why measuring a broken spring is still possible

A spring that has broken in half is still measurable. The two halves of a broken torsion spring add up to the original length when placed end-to-end, minus the space created by the break. Add about 1/4 inch to the combined measurement of both halves to get the original spring length. Wire diameter is unchanged by the break and can be measured anywhere along either half. Inside diameter is also unchanged.

If only one spring broke but you have a two-spring system, measure the intact spring. Left-wound and right-wound springs on the same door are usually the same wire diameter and length even though their winding direction is opposite. Confirm by measuring both halves of the broken spring against the intact one.

Before ordering, double-check that you know whether you have a torsion spring (horizontal coil above the door mounted on a bar) or extension springs (long springs running along the side tracks). The measurement method above applies to torsion springs. Extension springs use a different specification: you measure the relaxed (unstretched) wire diameter and the stretched (installed) length, then match the DASMA color code to the door's weight. An incorrectly matched extension spring can snap under load, so if you are unsure which type you have or cannot get a clean measurement, have a technician handle the specification.

Also note the spring force rating, which some suppliers list alongside the three dimensions. For a two-spring torsion system, the spring force is divided between the two springs. A single-spring system places the full load on one spring and typically requires a heavier wire diameter or longer spring. If your door originally had two springs and you are replacing with one (or vice versa), the spring specifications change, so you cannot simply copy the dimensions from one of the original springs.

G Brothers handles spring measurements, ordering, and installation for Denver and Front Range homeowners. If you are not comfortable measuring with calipers or are unsure which spring you need, we can handle the full job with same-day service and free estimates. We stock the most common residential spring sizes and can order specialty sizes quickly.