A heat shrink tubing size chart gives you three numbers: expanded ID, recovered ID, and recovered wall thickness. If you know what each one means, you can pick the right size in under a minute. If you don't, you'll end up with tubing that's too loose to seal or too tight to slide on. This guide explains how to read the chart and avoid both problems.
The Three Numbers That Matter
Expanded ID is the internal diameter of the tubing as you receive it — before any heating. This is the number that determines whether the tubing will fit over your cable, connector, or splice. If the expanded ID is smaller than the largest diameter you need to pass over, the tubing won't go on.
Recovered ID is the internal diameter after the tubing has fully shrunk. This determines whether the tubing will grip the object tightly. If the recovered ID is larger than the smallest diameter you're sealing onto, the tubing will be loose.
Recovered wall thickness tells you how much mechanical and electrical protection you get after shrinking. Thicker walls resist abrasion and provide higher dielectric strength, but they also make the assembly stiffer.
How to Measure Before You Order
Measure the actual cable or part, not the wire gauge number.
AWG defines the conductor diameter, but the insulation thickness varies by manufacturer and voltage rating. Two cables labeled "12 AWG" can have outer diameters that differ by 0.5 mm or more. That difference can be the difference between a snug fit and a loose sleeve.
Use calipers and measure at three points along the cable — at the end, 50 mm in, and 100 mm in. Cables are not perfectly round, especially after being coiled on a drum. Take the largest of the three readings as your "pass-over diameter."
Then measure the smallest diameter you need the tubing to seal onto — usually the cable jacket itself, not the connector.
The 80% Rule for a Tight Fit
The recovered ID should be no more than 80% of the smallest diameter you're sealing onto. This leaves 20% of shrinkage margin to ensure the tubing grips tightly rather than just resting on the surface.
For example, if you're sealing onto a cable with 5.0 mm outer diameter, you need tubing with a recovered ID of 4.0 mm or less. At the same time, the expanded ID must be at least 20% larger than your largest pass-over diameter.
Metric vs AWG Cross-Reference
| Size (mm) | AWG (approx.) | Fractional (approx.) | Typical Use |
|---|---|---|---|
| 1.2 / 0.4 | 22-26 | 3/64 | Fine wire, sensor leads |
| 2.4 / 0.9 | 18-20 | 3/32 | Signal wire, small splices |
| 3.4 / 1.4 | 16-18 | 1/8 | Power wire, automotive |
| 5.4 / 2.3 | 12-14 | 3/16 | Battery cable, harness |
| 8.4 / 3.8 | 8-10 | 1/4 | LV cable, busbar |
| 10.5 / 4.8 | 6-8 | 5/16 | LV cable, connectors |
| 15.5 / 7.2 | 2-4 | 3/8 | Multicore cable |
| 21.0 / 9.7 | 500 MCM | 13/16 | Power cable joints |
| 30.8 / 14.0 | — | 1-3/16 | HV cable, large joints |
| 51.0 / 24.0 | — | 2 | Large cable repair |
Note: this table shows expanded ID / recovered ID for our LRS-1 series (2:1 ratio). The AWG column is approximate because insulation thickness varies by manufacturer. Always measure your actual cable before ordering.
FAQ
Why does my 2:1 tubing not shrink tight enough?
The recovered ID is probably larger than 80% of your cable's outer diameter. Check the size chart for your tubing's recovered ID, then measure your cable with calipers. If the cable is at the lower end of the tubing's range, the tubing may not have enough shrinkage left to grip tightly.
Can I use a larger size and just let it shrink more?
No. Heat shrink tubing shrinks to a maximum percentage of its expanded ID, not to any arbitrary diameter. A 2:1 tubing with 10 mm expanded ID will only shrink to 5 mm recovered ID — it won't shrink further to grip a 3 mm cable.
Do fractional sizes and metric sizes match exactly?
Not always. A "3/32 inch" tubing (2.38 mm) is close to but not exactly the same as a 2.4 mm metric size. When ordering, specify metric dimensions if your design uses metric cable, and vice versa. Don't convert between systems by rounding.
Written by Long, Sales Engineer at ZZ Heat Shrink. For a full size chart covering all 28 standard sizes from 0.8 to 50 mm, see single wall heat shrink tubing. For a quotation, contact our engineers.