Before you choose a camera head, it helps to know the pipe you will actually inspect. Homes in the United States use a small set of common pipe diameters, and each one favours a different head. This page walks through those sizes, what lives at each one, and how the diameter drives head choice. The nameplate size on a fitting is only a starting point, because the inside diameter and the fittings decide what really passes.
The common residential diameters
Branch lines under a sink, basin, or toilet often run 1.5 to 2 inches. These are the tightest runs in a house, with sharp elbows close together. A small 17mm head is usually the only size that turns them without wedging.
House drain lines and short laterals commonly sit at 3 to 4 inches. This is the everyday range for residential inspection. A 23mm or 25mm head suits it well, small enough to pass a cleanout yet large enough to stay centred so the light spreads evenly.
Main sewer lines and larger laterals reach 4 to 6 inches, sometimes wider. Here a larger head earns its size, because a small head drifts along the bottom and leaves the pipe crown dark. A head sized to the pipe, ideally self levelling, rides closer to the middle.
Nameplate size versus inside diameter
Pipe is sold by a nominal size, but the inside diameter is what your camera travels. Wall thickness, the pipe material, and old scale or grease all shrink the usable bore. A nominal 2 inch line can be tighter inside than the label suggests, especially in older cast iron. So treat the nameplate as a guide and give yourself margin, rather than sizing a head to the exact printed number.
How diameter drives head choice
| Pipe diameter | Typical location | Suited head |
|---|---|---|
| 1.5 to 2 in | Branch lines, fixtures | 17mm |
| 3 to 4 in | House drains, short laterals | 23 to 25mm |
| 4 to 6 in | Mains, larger laterals | 25 to 30mm |
When a single run mixes sizes, for example a 2 inch branch feeding a 4 inch stack, size the head to the smallest section it must pass, not the widest. A head that clears the tightest point will still work in the wider pipe, even if it sits a little low there.
Fittings matter as much as diameter
Two lines of the same diameter can behave very differently. Long sweep bends let a head glide, while tight quarter bends and back to back fittings grab it. Older homes tend to have sharper fittings and more of them. If your line is full of tight turns, lean toward a smaller head and a cable that flexes, even in pipe that would otherwise take a larger head.
Map your pipe to the right tool
Rather than trust a generic 2 to 4 inch marketing icon, measure or estimate your real diameters and match them to a head from the specification data. The pipe size checker turns a diameter into a head class, and the head size reference shows what each option does. That two step check beats guessing from a product listing, and it stops you buying a head that jams or one that sees too little.
Access points shape the job
Diameter decides the head, but where you enter the pipe decides how easily you reach it. A cleanout gives a straight, roomy start, so a head passes without fighting a trap. Entering through a removed toilet or a roof vent adds tight turns before the head even reaches the drain. The same 4 inch line can feel easy from a cleanout and awkward from a fixture, so think about your access point when you pick a head and cable, not just the pipe size on paper.
When to size down
If your home is older, has many fixtures on short branch lines, or mixes cast iron with newer plastic, lean toward a smaller head than the nominal diameter alone would suggest. Scale narrows old pipe, sharp fittings grab a large head, and a stall deep in the line is far more trouble than a slightly lower view. A 17mm head that clears everything beats a 25mm head that reaches the first tight bend and stops. Size for the worst point on the run, then enjoy the easy sections.
Frequently asked questions
What is the most common residential drain size?
Most house drains and short laterals run 3 to 4 inches. That range is the everyday target for inspection, and a 23 to 25mm head suits it well. Branch lines are narrower, and mains can be wider.
Can I inspect 2 inch and 4 inch pipe with one head?
Yes, with a 17mm head. It clears the 2 inch branches and still returns a usable picture in 4 inch line. The compromise is that it sits low in the wider pipe, so a dedicated 4 inch head would see more there.
Does pipe material change head choice?
It can. Old cast iron often has scale that narrows the bore and rougher walls that grab a head, so a smaller head and a flexible cable help. Smooth plastic pipe is more forgiving and lets a larger head pass cleanly.