Our resin saddle bands and resin pipe clamps need to be selected according to the outside diameter (mm) of the object being installed, choosing a product with the appropriate compatible diameter Ø (mm). For that reason, we recommend measuring the outside diameter accurately first in order to choose the correct size. This page summarizes the basics of how to measure the outside diameter, focusing on round pipes.
What you’ll learn in this article
- Basic concepts for measuring pipe outside diameter correctly
- How to measure outside diameter with calipers or a tape measure
- How to calculate outside diameter from the circumference
- Points to note when attaching to oval or square pipes
The relationship between outside diameter and compatible diameter
The size notation for our products, compatible diameter Ø (mm), refers to the outside diameter of the object being installed (the outer diameter of pipes, rods, etc.). If there is a difference between the object’s outside diameter and our product’s compatible diameter, the following issues may occur.
- Insufficient holding power (vibration isolation and anti-slip effects cannot be achieved)
- Too tight to fit, so it cannot be installed
For that reason, we recommend choosing based on actual measurements whenever possible.
* Nominal diameter (A) is a designation used in piping standards and often does not match the outside diameter. The relationship between nominal diameter and outside diameter is explained in detail in a separate article: What is pipe nominal diameter? A size-by-size explanation of how it differs from the outside diameter.
How to measure the outside diameter of a round pipe
How to directly measure the outside diameter with calipers (recommended)
Calipers are the most accurate tool for measuring outside diameter. If precision matters, we recommend using calipers.
- Lightly wipe off any dirt from the pipe surface
- Gently place the caliper jaws on the outside of the pipe
- Choose a spot that is close to perfectly round, and secure it where the jaws make contact firmly but not too tightly, with no gap
- Read the caliper scale (or digital display)
How to measure the circumference with a tape measure and calculate the outside diameter
You can measure the circumference with a tape measure and then calculate an approximate outside diameter by formula.
- Wrap the tape measure all the way around the pipe once
- Read the length (circumference) at the point where it comes full circle
- Formula: circumference (mm) ÷ 3.14 = approximate outside diameter
(Calculation example)
If the circumference is 85mm: 85 ÷ 3.14 ≒ 27.07mm
→ Please choose a product with compatible diameter Ø27mm (vibration isolation type) or Ø27.2mm (standard type).
* It is easier to select a product if you calculate to one decimal place and use the rounded value as the reference.
How to measure oval and square pipes
Our resin saddle bands, resin pipe clamps, and similar products are basically designed for round pipes. However, vibration isolation types may also be usable on oval or square pipes in some cases.
For oval pipes
- Measure the long diameter (the longer side) with calipers, a ruler, or similar tool
- Choose the compatible diameter based on the long diameter
* If the oval shape is too elongated, the contact area of the product may be insufficient, and adequate holding power may not be achieved.
For square pipes
- Measure the diagonal length (mm) of the square pipe
- Or calculate an approximate diagonal using "one side length × 1.41 (√2)"
- Use the diagonal length as a guide and choose a compatible diameter that is two sizes smaller
(Calculation example) If one side is 15mm
15mm × 1.41 ≒ about 21mm
→ Compatible diameter Ø19mm is recommended.
Measurement error and allowable range
The outside diameter of a pipe may vary depending on differences in manufacturers and standards, expansion and contraction due to temperature changes, and whether it has been painted or wrapped with tape.
Selection guide
For our products, choose a compatible diameter Ø (mm) within ±0.3mm of the actual measured outside diameter (mm). If the difference is ±0.4mm or more, it may be too tight to install, or may be more likely to shift.
Also, for vibration isolation types, compatible diameter adjustments can be made in 0.5mm increments. For details, see How to request compatible diameter adjustments (vibration isolation type) article.
Summary
- Be sure to check the actual outside diameter (mm), not the nominal diameter (A).
- Based on the actual outside diameter (mm), choose the appropriate compatible diameter Ø (mm) product.
If you’re not sure (Contact us)
If you provide the following information, we will recommend the compatible diameter and product that best suits your needs.
- Outside diameter of the object (mm, to one decimal place if possible)
- Type of pipe (e.g., PVC pipe, steel pipe, other piping-standard pipes)
- Where you want to install it (e.g., indoors, outdoors, wall, ceiling)
- Expected load and usage environment (e.g., presence of vibration, outdoor exposure)
Related articles
- What is pipe nominal diameter? A size-by-size explanation of how it differs from the outside diameter
- Piping size chart | Quick reference for nominal diameter and actual outside diameter of PVC pipe (VP) and more
- Resin saddle band size selection guide | Why you should choose based on outside diameter, not nominal diameter
- Resin pipe clamp size selection guide | How to choose based on the pipe’s outside diameter