Most people think a half-inch copper pipe are half an inch wide. They are wrong. A lot of DIY plumbing mistakes results from this confusion between nominal (historically meaningless) size and actualy (meaningful) size. The half-inch fittings you purchase is intended to fit pipes whose outside dimension is about five-eighths of an inch across.
Use the chart to see what’s what; and not guess when shopping. Why does it matter? You might order wrong size by mistake; then your seals won’t work, or you’ll have to return items to store.
How to Choose Copper Pipe Size and Type
There are three primary types of water-supply tubing with different wall thicknesses. The thickest is Type K, which marked green. Use this underground or in places where it might be crushed by the earth or otherwise impacted. Medium thick (blue marked) is Type L, which strike a good balance between easy bending and ability to withstand pressure. It is most common for indoor supply tubing in homes. Plumbers will typicaly choose it when doing rough-in installation in a residence.
The thinnest one (marked in red) is Type M. It is good for use under low pressure, such as in a rough-in installation in a residence, where high pressure isn’t required. Don’t bury it underground because rocks can easly damage it.
So when do you choose one over another? That’s all about risk and money. A bigger wall means there is more copper in there (duh). This makes your total cost of materials go up, and the ID of same nominal size will be smaller. But that added metal mean it won’t corrode as much on the outside and it will last longer before being punctured.
You are running a line through concrete slab. Probably go with Type K. Is the bathroom vanity inside drywall? No problem, go with Type M. It’s not as hot to solder. You will have fewer flux burning problems and neater joints if you’re new to this. And some folks swear by the thicker the better. The thing with the thinner walls though: they heats up quicker when you’re trying to solder them. There is less chance of burnt flux issues and you get cleaner joints.
Also be aware of DWV copper (DWV = drain waste and vent). This is for all tubing that carries away gravity-fed water but not pressurized water. It’s large diameter and very thin wall. It is never used on supply lines, since they’d blow out under pressure. It is used only for safely removing water from home. Type K is more like a solid rod with a tiny center hole, whereas DWV is more like a hollow tube with hardly any stuff inside. The key to avoiding deadly errors such as pressurizing a drain line by mistake are keeping them separate in your mind.
In the past ten years, joining methods has evolved considerably. The old-school method of sweat soldering is still popular; it’s tried-and-true, and relatively inexpensive. Clean pipe, put some flux on it, heat up your fitting and throw down a bead of solder. It forms a lasting seal and can stay effective for decades when done propery. But there has been an increasing trend toward press-fit technology with pros who prioritize efficiency. Press-fit connectors need a special crimping tool, but completely remove any open flame from the equation. You also won’t have to worry about fire permits around wood or drywall. For pipes carrying gas or refrigerants, flared connections continues to dominate because they’re reusable and don’t depend on melted metal to make connection. Each technique offers something to suit different preferences for safety, speed, or permanence.
Why does copper stay so popular? It resists corrosion and prevents bacteria growth within your home’s walls. It pays for itself with longevity. You should of considered the cost. The next time you notice colored stripes painted on pipes, realize those are codes that show the stress level that particular pipe can withstand. Don’t choose by sticker price, instead select the thickness suitable for environment.
Incorrectly fitting a joint is an expensive repair; even more so when concealed within walls. Size matter. Select correct wall thickness to get job done right and enjoy the durability. The half-inch label is simply a name; it’s the metal itself that reveals the specs.
