Schedule 40 Pipe Thickness in mm & Inches: Complete Size Chart

Schedule 40 Pipe Thickness varies according to the nominal pipe size. It is not one fixed thickness for every pipe. For example, a 2-inch Schedule 40 steel pipe has a nominal wall thickness of 3.91 mm (0.154 inch), while a 4-inch pipe has a wall thickness of 6.02 mm (0.237 inch).

Schedule 40 is one of the most commonly specified pipe schedules for steel piping. It is used in water lines, plumbing, construction, process piping, compressed air systems, and many general industrial applications.

This guide explains Schedule 40 pipe thickness in mm and inches, with NPS and DN equivalents, outside diameter (OD), approximate inside diameter (ID), pipe weight, material considerations, and commonly requested sizes.

Schedule 40 pipe thickness is the nominal wall thickness assigned to a particular nominal pipe size.

The important point is that Schedule 40 does not represent a single wall measurement. The thickness changes with the pipe's nominal size.

For example:

Therefore, when someone asks for the SCH 40 Pipe Thickness, the pipe size must also be specified.

The schedule should be considered together with the applicable pipe dimensional and product standard when selecting or ordering pipe.

The term Schedule 40 identifies a standardized pipe wall-thickness designation.

For a given nominal pipe size, the outside diameter is standardized. Changing the schedule generally changes the wall thickness and therefore changes the available inside diameter.

For example, a 2-inch steel pipe has an outside diameter of 60.3 mm. A thicker schedule uses more of that diameter for the pipe wall, leaving a smaller internal opening.

This is why Schedule 80 pipe is generally thicker than Schedule 40 pipe of the same nominal size.

Schedule Number vs Pipe Size

It is important not to confuse the schedule with the pipe diameter.

• NPS identifies the nominal pipe size.
• DN provides a metric nominal designation.
• Schedule identifies the wall-thickness designation.
• OD is the standardized outside diameter.
• ID is the internal diameter after accounting for wall thickness.

The following chart provides common Schedule 40 steel pipe dimensions, including NPS, DN, outside diameter, nominal wall thickness, and approximate inside diameter.

Note: The inside diameter shown is approximate and is calculated from the outside diameter and nominal wall thickness. Actual manufactured dimensions can vary within the tolerances permitted by the applicable product standard.

Schedule 40 Pipe Dimensions are normally described using NPS, DN, outside diameter, wall thickness, and inside diameter.

For example, a 2-inch Schedule 40 pipe has:

• NPS: 2 inch
• DN: DN50
• Outside diameter: 60.3 mm
• Wall thickness: 3.91 mm
• Approximate inside diameter: 52.5 mm

The basic relationship is:

Approximate ID = OD − (2 × Wall Thickness)

Using the 2-inch example:

60.3 − (2 × 3.91) = 52.48 mm

Therefore, the approximate internal diameter is 52.5 mm.

This relationship is useful when checking pipe dimensions, calculating flow areas, or estimating internal volume.

Pipe weight depends primarily on its dimensions and material density. For steel pipe, larger diameters and thicker walls generally result in greater weight per metre.

These are approximate theoretical values for carbon steel pipe. Actual pipe weight can vary because of material density, manufacturing tolerances, and product specifications.

For stainless steel, the weight will differ because stainless steel has a different material density.

The main difference between Schedule 40 vs Schedule 80 is the wall thickness. For the same nominal pipe size, Schedule 80 generally has a thicker wall than Schedule 40.

A thicker schedule can provide greater pressure capability under otherwise comparable conditions, but pressure capacity should not be determined from the schedule alone.

There is no single pressure rating that applies to every Schedule 40 pipe.

The allowable pressure depends on factors such as:

• Pipe material
• Material grade
• Pipe size
• Wall thickness
• Operating temperature
• Allowable stress
• Design code
• Corrosion allowance
• Joint or welding requirements
• Application

For example, the pressure capability of carbon steel Schedule 40 pipe cannot be assumed to be the same as PVC Schedule 40 pipe.

For pressure-service applications, always use the relevant design code and manufacturer's technical data rather than relying on a generic pressure value.

Schedule 40 pipe is commonly selected for applications where its dimensional and mechanical characteristics meet project requirements.

Typical applications include:

The appropriate pipe material and schedule should always be selected according to the operating conditions and applicable design requirements.