Understanding Sewer Pipe Sizes and Schedules: A Comprehensive Guide

Different Types of PVC Fittings

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Whether you’re installing a dishwasher or adding an entire plumbing system to new construction, you must understand the different sewer pipe sizes and schedules at your disposal. Pipe dimensions differ depending on the material and schedule.

The schedule number allows you to properly define a pipe’s thickness before ordering or using it in your plumbing project. In the past, pipes were only available in three sizes, which included standard weight, extra-strong, and double extra-strong. They are now outfitted with a schedule number that takes pressure and temperature conditions into account.

What Is Pipe Scheduling?

The scheduling of a pipe refers to pipe wall thickness. To make it easier for pipes to be ordered, the American Society of Mechanical Engineers (ASME) created a “schedule number”, which tells you the value of 1,000 x P/S. The P stands for service pressure, while the S stands for allowable stress. Both numbers are displayed in pounds per square inch.

While pipe scheduling isn’t an actual measurement, it serves as a guide number that indicates the thickness of a pipe wall. Separate pipes can have the same diameter while having different schedules, which means that the wall thicknesses of these pipes are different.

By using pipe scheduling to identify the proper PVC sewer pipe sizes you should use for your project, you’ll effectively limit the number of mistakes you make when completing an order.

Schedule 40 vs. Schedule 80: The Basics

Two of the most common sewer pipes are Schedule 40 and Schedule 80 pipes. While Schedule 40 pipes are usually silver or white, you can find them in many different colors. These pipes have a relatively thin wall in comparison to Schedule 80 pipes, which makes it possible for liquid to get through them at a faster rate.

Even though the walls are thinner, they are highly heat resistant and can withstand a substantial amount of pressure. Schedule 40 PVC pipe dimensions range from .068 to .688 inches in wall thickness. These pipes are often used as drainage for buildings. Consider Schedule 40 pipes when working with potable water lines, gas lines, pools, or golf course construction projects.

Schedule 80 pipes have a higher thickness than Schedule 40 ones. While Schedule 80 PVC pipe isn’t the thickest option around, its dimensions range from 0.95 to 1.2 inches in thickness. These pipes can withstand up to 1,230 PSI of pressure.

Most Schedule 80 pipes are dark grey. They are commonly used for chemical processing, deionized water lines, wastewater treatment management, and industrial plating. At Lesso, we provide a variety of PVC sewer pipe sizes to ensure you have the high-quality pipes you need for your next plumbing project.

Importance of Fitting Sizing

Regardless of the type of plumbing project you’re working on, correct fitting sizing is essential. The success of your project may depend on how accurate your measurements are for your pipes and fittings. Let’s say you’re working on a large home renovation project and are redoing the entire plumbing system. If you don’t obtain the correct fittings, you could end up completing 80% of the project before you find that certain pieces don’t fit together.

To arrive at the proper pipe measurements, there are a couple of parameters you should understand, which include Nominal Pipe Size (NPS) and Outer Diameter (OD). The NPS designation is dimensionless and is mainly used to indicate the standard size of a pipe. It doesn’t use an inch symbol. When looking at a Schedule 40 steel pipe, NPS 6 has an outside diameter of 6.625 inches.

To measure NPS, focus on identifying the threads per inch and circumference of the pipe. When handling male pipe threads, the circumference must be measured at the widest point. For female pipe threads, calculate the inside diameter around the widest point.

As for the outer diameter (OD), this is the measurement of a circular pipe’s outside edges. By combining the pipe’s outer diameter with the wall thickness, you’ll arrive at an accurate calculation.

Factors to Consider:

Pressure and Thickness

Two of the most important factors to consider when buying pipes are pressure and thickness. Different schedules have different pressure ratings. For example, PVC-U Schedule 40 Pipe Fittings, as a 1/2-inch Schedule 40 pipe has a maximum pressure of 5,792 PSI. In comparison, the PVC Schedule 80 Pipe fittings with the same 1/2-inch size have a maximum PSI of 8,140. Pipes that have better wall thicknesses can handle more pressure without cracking.

Cost Implications

Because of the thinner walls, Schedule 40 pipes are invariably cheaper than Schedule 80 pipes. The type of material you choose determines the overall costs you pay. Keep in mind that PVC pipes are often more expensive to make than steel pipes. However, PVC pipes have better corrosion resistance and are easier to install. Lesso’s range of pipes offers high value for your money.

Color Coding and Identification

As touched upon previously, different pipe schedules are noted with different colors. Schedule 40 pipes often come in white or silver, while Schedule 80 pipes are gray. Color coding is used to limit the possibility of making a mistake while ordering pipes for your plumbing project. It’s crucial that you properly identify the correct size and type of pipe before you make your purchase. All Lesso pipes are marked.


Sewer pipes are available in many different sizes and wall thicknesses. Even if the diameter of two pipes is the same, the wall thickness could be different, which is why you need to obtain accurate measurements before buying Schedule 40 or Schedule 80 piping.

If you need help choosing the right schedule and size, Lesso is a reliable provider of drainage and sewer pipes that can assist you in this regard. Call Lesso today to get started.

FAQs about Sewer Pipe

Temperature can impact the pressure rating of a pipe, which in turn affects its scheduling. For instance, a Schedule 40 pipe may be suitable for a certain application at room temperature but may require upgrading to Schedule 80 in higher temperatures.

Yes, pipe scheduling is standardized by organizations like the American National Standards Institute (ANSI) and American Society for Testing and Materials (ASTM). These standards ensure uniformity and reliability across different manufacturers, including Lesso.

While it’s technically possible, mixing different schedules in a single system is generally not recommended due to differences in wall thickness and pressure ratings. Always consult with a professional to ensure compatibility.

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