How to Measure Your Exhaust Pipe

In the world of high-flow exhaust, size really does matter, and not just for the sights and sounds. Naturally, the components should fit together to work well. While you might know your ride’s horsepower off the top of your head, most of us just scratch our heads when it comes to exhaust diameters. Fortunately, sizing up your system is easier than you think. Check out this quick guide for straightforward advice on figuring out what kind of pipes you’re packing.

Outside Diameter vs. Internal Diameter

There are two types of measurements to pay attention to when you’re working with tubing — the external diameter and the internal diameter. The external diameter is the distance from edge-to-edge, including the thickness of the tube itself. The internal diameter is the distance from edge-to-edge, not including the tube thickness. So, just the space inside.

Generally, exhaust tips and mufflers use an internal diameter measurement because they usually slip over the exhaust pipe. Most exhaust piping uses an external diameter measurement. Why? Because it fits inside a muffler or tip.

How to Measure Outside Diameter

If the end of the pipe is fully exposed (not covered by an exhaust tip or fitted into a muffler), use a tape measure or ruler to measure. Remember, you’ll be measuring from one outside edge to the opposite outside edge, across the center point.

If the end of the pipe is blocked, use a pair of dial calipers to measure the distance. If the end of the pipe is blocked and you don’t have a pair of dial calipers handy, you can use a bit of arithmetic instead. First, find the circumference of the pipe using a tailor’s measuring tape (or a piece of string you can then measure with a standard measuring tape or ruler). Then, divide the circumference by π (3.14) to get the outside diameter.

How to Measure Internal Diameter

If the end of the pipe is exposed, use a tape measure or ruler to measure the distance from the inside edge to the opposite inside edge through the center point. For a more precise measurement, use a pair of dial calipers.

If the end of the pipe isn’t exposed, you’ll have to cut the pipe to take a proper measurement.

Inlet vs. Outlet

Exhaust fumes flow in one direction — from your engine back to the tailpipe. Some exhaust systems use different diameter tubing at different points along the path. For example, the tubing between the exhaust manifold and muffler might start at 2.5”, but then it might switch to 3” for the tailpipe. When you’re taking your measurements, make sure to check both the inlet sizes (the section pointing towards your engine) and outlet sizes (the section pointing towards your tailpipe).

How to Connect Exhaust Components

When one section of pipe fits inside another section, it creates a lap joint. You can use a band clamp or U-bolt to secure the connection or you can weld the joint for a leak-free fit. Many exhaust tips have band clamps built right in, but you can always weld for extra security. When two sections of pipe are the same outside diameter, they create a butt joint. Band clamps and welding are the only options for making a secure connection.

Remember, if you ever have any questions about finding an exhaust component that fits, we have answers. Our expert pit crew is here to help you find the right gear for your ride.