Inside diameter of 1 inch pvc pipe

In plumbing projects, the size marking of PVC pipes is often confusing, especially the difference between the actual inside diameter of “1-inch PVC pipe” and the nominal size. This article will comprehensively analyze the Inside diameter of 1 inch PVC pipe standards, measurement methods and purchase considerations to help you accurately select and apply.

Dimension standards for 1-inch PVC pipes

(1) Nominal size and actual size

Nominal size: 1 inch (abbreviated as “1” or “DN25”) is the “nominal size” of the pipe, not the actual measurement value.

Actual inside diameter (ID): varies depending on the pipe type and standard:

PVC Pipe Type	Actual ID (Inner Diameter)	OD (Outer Diameter)	Wall Thickness
Schedule 40 PVC	26.64 mm	33.40 mm	3.38 mm
Schedule 80 PVC	24.30 mm	33.40 mm	4.55 mm
PVC Conduit (EMT)	27.00 mm	32.50 mm	2.77 mm

 

Note:

1 inch = 25.4 mm, but the inner diameter of PVC pipe is usually larger or smaller than this value.

DN25 is a metric mark, corresponding to 1 inch in the imperial system, but the inner diameter may be different.

(2) Why is the inner diameter ≠ 1 inch?

Historical reasons: Following the metal pipe standard, the outer diameter of PVC pipe is consistent with that of metal pipe to ensure compatibility, but the different wall thickness leads to changes in the inner diameter.

Pressure requirements: Schedule 80 pipes have thicker walls, smaller inner diameters, and higher pressure resistance (suitable for industrial scenarios).

How to measure the inside diameter of 1 inch PVC pipe?

(1) Tool preparation

Vernier caliper (accuracy 0.1mm)

Tape measure or ruler (rough measurement)

(2) Measurement steps

Confirm the pipe type: Check the pipe body marking (such as “Schedule 40” or “DN25”).

Clean the pipe mouth: Remove burrs or dirt.

Measure the inside diameter: Use a caliper to measure vertically at the pipe mouth 3 times and take the average value.

Comparison standard: Check with the data in the table above to determine whether it meets expectations.

Example: If the measured inside diameter is 26.6mm, it is a Schedule 40 PVC pipe.

Application scenarios of 1-inch PVC pipes

(1) Schedule 40 (general purpose)

Water supply and drainage systems: household tap water, rainwater drainage (large inner diameter, sufficient flow).

Agricultural irrigation: branch pipes connected to sprinklers or drip irrigation belts.

Applicable pressure: ≤150 PSI (about 1.03 MPa).

(2) Schedule 80 (industrial type)

Chemical pipelines: transport corrosive liquids (wall thickness is pressure-resistant and impermeable).

Compressed air system: air supply for factory pneumatic equipment.

Applicable pressure: ≤200 PSI (about 1.38 MPa).

(3) PVC wire and cable (EMT)

Electrical engineering: protect cables (27mm inner diameter can pass multiple cables).

Features: flame retardant, insulating, no need to bear pressure.

Things to note when purchasing 1-inch PVC pipe

(1) Clarify your needs

Fluid type: water/gas/chemicals? Schedule 80 is more corrosion-resistant.

Pressure requirement: Schedule 80 for high pressure and Schedule 40 for low pressure.

Installation method: Adhesive (PVC-U) or threaded connection (PVC-M)?

(2) Verify the size

Ask the supplier to provide the actual measured inner diameter data to avoid mismatch with the accessories.

Check the pipe body marking: such as “ASTM D1785” (Schedule 40 standard).

(3) Matching accessories

Elbows, tees and other accessories must be of the same type and specification as the pipe (such as Schedule 40 with Schedule 40 connector).

FAQ

Q1: Can a 1-inch PVC pipe be inserted into a 1-inch metal pipe?

A: Yes! Because the outer diameter is the same (33.4mm), but please note:

The metal threaded interface needs to be matched with a PVC transition joint.

It cannot be directly welded, and flanges or clamps must be used for connection.

Q2: Will the difference in inner diameter affect the flow rate?

A: Yes! The smaller the inner diameter, the faster the flow rate but the flow rate is reduced. For example:

Schedule 40 (ID 26.6mm) has a flow rate that is about 20% higher than Schedule 80 (ID 24.3mm).

Q3: Are DN25 and 1-inch PVC pipe the same thing?

A: Nominally equivalent, but the actual inner diameter may vary slightly depending on the standard (for example, the inner diameter of the European standard DN25 may be 27mm).

Inside diameter of 1 inch pvc pipe varies depending on the type:

Schedule 40: 26.64 mm (general drainage/water supply).

Schedule 80: 24.30 mm (high voltage/industrial scenarios).

Wire conduit: 27.00 mm (electrical protection).