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Pi Tape® Precision Diameter Measuring Tapes


Pi Tape® precision diameter measuring tapes provide a quick, accurate and easy method of measuring the outside diameter of cylindrical, round and out-of-round parts. Also commonly called diameter tapes, diameter measuring tapes or precision vernier diameter tapes, Pi Tapes convert the circumference of a part into a direct diameter reading.


Newman Tools supplies Pi Tape® measuring tapes in inch and metric sizes, including standard outside diameter tapes, large-diameter tapes and specialty Pi Tape products. We ship worldwide, including Canada and the USA.

Pi Tape precision diameter measuring tape being used to measure outside diameter
 
 
 

What Is a Pi Tape®?

A Pi Tape is a precision measuring tool used to determine the diameter of a cylindrical object by measuring its circumference. The graduations on the tape are calculated so that the user can read the diameter directly rather than measuring the circumference and performing a separate calculation.

Pi Tape® periphery tapes provide a quick and accurate way of reading true diameters of both round and out-of-round forms. They are especially useful for thin- or soft-walled parts, large components and applications where a conventional outside micrometer or caliper is impractical.

  • Precision measurement of cylindrical and round components.
  • Useful for thin- or soft-walled parts, large or small.
  • Graduations convert circumferential distance directly into diameter.
  • Standard tapes are checked over master gages to the manufacturer's specified accuracy.
  • Calibration documentation traceable to NIST is furnished with each new tape.
Accuracy: Standard Pi Tapes up to 144 inches (3600 mm) are checked over master gages at .001 inch (.03 mm) accuracy. Always use the manufacturer's specified tension and measuring procedure when maximum accuracy is required.
 

Pi Tape Materials

Standard outside diameter Pi Tapes are supplied in 1095 clock spring steel unless another material is specified.

 Stainless steel versions are available for applications where corrosion resistance is required. Ideal for oil & gas, pipeline, and marine applications.

Pi Tapes require little maintenance. After use, wipe the tape clean and apply a light rust preventive oil. Do not bend, kink or step on the tape, as damage can affect measurement accuracy.

 

Pi Tape Applications

Pi Tapes are commonly used for:

  • Machine shop inspection and quality control
  • Measuring shafts, cylinders and turned parts
  • Pipes and plastic pipe
  • Rollers and thin-walled components
  • Large fabricated components
  • Aerospace and manufacturing applications
  • Maintenance and repair
  • Production and inspection applications requiring direct diameter readings
 
 
 

Inch Pi Tapes — Outside Diameter

The standard inch Pi Tape range covers diameters from 1/2 inch through 144 inches. The PI-1 covers 2 to 12 inches and is one of the standard sizes commonly used for machine-shop and inspection applications.

Part No. Outside Diameter Measuring Range Description
PI-0001/2–2"0.500 to 2" Diameter Tape
PI-013/4–7"0.75 to 7" Diameter Tape
PI-12–12"2 to 12" Diameter Tape
PI-1SP2–24"2 to 24" Diameter Tape
PI-212–24"12 to 24" Diameter Tape
PI-2SP12–36"12 to 36" Diameter Tape
PI-324–36"24 to 36" Diameter Tape
PI-3SP24–48"24 to 48" Diameter Tape
PI-436–48"36 to 48" Diameter Tape
PI-548–60"48 to 60" Diameter Tape
PI-660–72"60 to 72" Diameter Tape
PI-772–84"72 to 84" Diameter Tape
PI-884–96"84 to 96" Diameter Tape
PI-996–108"96 to 108" Diameter Tape
PI-10108–120"108 to 120" Diameter Tape
PI-11120–132"120 to 132" Diameter Tape
PI-12132–144"132 to 144" Diameter Tape

Standard clock steel will be supplied unless specified otherwise. For current pricing and availability, see the Pi Tape Price List.

 

Metric Pi Tapes — Outside Diameter

Metric Pi Tapes are available for outside diameter measurements from 28 mm through 3600 mm, with standard and extended ranges.

Part No. Outside Diameter Measuring Range
PI-M-028–200 mm
PI-M-1100–300 mm
PI-M-1SP50–600 mm
PI-M-2300–600 mm
PI-M-2SP300–900 mm
PI-M-3600–900 mm
PI-M-3SP600–1200 mm
PI-M-4900–1200 mm
PI-M-51200–1500 mm
PI-M-61500–1800 mm
PI-M-71800–2100 mm
PI-M-82100–2400 mm
PI-M-92400–2700 mm
PI-M-102700–3000 mm
PI-M-113000–3300 mm
PI-M-123300–3600 mm

Standard clock steel will be supplied unless specified otherwise. Stainless steel versions may be ordered by adding SS to the part number, subject to the manufacturer's current material and size specifications.

 
 

Extra Large Diameter Inch Pi Tapes — Over 144"

Extra-large diameter Pi Tapes are available by special order for applications above 144 inches in outside diameter. Standard tapes are manufactured with a 1/4" wide Vernier gage, a 1/2" wide main body and a 1/4" wide gage member.

Diameter Range O.D.Part No.
144–156"P13
156–168"PI-14
168–180"PI-15
180–192"PI-16
192–204"PI-17
204–216"PI-18
216–228"PI-19
228–240"PI-20
240–252"PI-21
252–264"PI-22
264–276"PI-23
276–288"PI-24
288–300"PI-25
300–312"PI-26
312–324"PI-27
324–336"PI-28
336–348"PI-29
348–360"PI-30
360–372"PI-31
372–384"PI-32
384–396"PI-33
396–408"PI-34
408–420"PI-35
420–432"PI-36
432–444"PI-37
444–456"PI-38
456–468"PI-39
468–480"PI-40
480–492"PI-41
492–504"PI-42
504–516"PI-43
516–528"PI-44
528–540"PI-45

Calibration reports traceable to NIST are furnished with each new tape at no additional charge. Manufacturer calibration and tolerance specifications apply.

 

Extra Large Diameter Metric Pi Tapes — Over 3600 mm

Diameter Range O.D.Part No.
3600–3900 mmPI-M-13
3900–4200 mmPI-M-14
4200–4500 mmPI-M-15
4500–4800 mmPI-M-16
4800–5100 mmPI-M-17
5100–5400 mmPI-M-18
5400–5700 mmPI-M-19
5700–6000 mmPI-M-20
6000–6300 mmPI-M-21
6300–6600 mmPI-M-22
6600–6900 mmPI-M-23
6900–7200 mmPI-M-24
7200–7500 mmPI-M-25
7500–7800 mmPI-M-26
7800–8100 mmPI-M-27
8100–8400 mmPI-M-28
8400–8700 mmPI-M-29
8700–9000 mmPI-M-30
9000–9300 mmPI-M-31
9300–9600 mmPI-M-32
9600–9900 mmPI-M-33
9900–10,200 mmPI-M-34
10,200–10,500 mmPI-M-35
10,500–10,800 mmPI-M-36
10,800–11,100 mmPI-M-37
11,100–11,400 mmPI-M-38
11,400–11,700 mmPI-M-39
11,700–12,000 mmPI-M-40
12,000–12,300 mmPI-M-41
12,300–12,600 mmPI-M-42
12,600–12,900 mmPI-M-43
12,900–13,200 mmPI-M-44
13,200–13,500 mmPI-M-45
 
 

How to Read a Pi Tape® Outside Diameter Tape

The Vernier scale allows the Pi Tape to provide a direct diameter reading. For the most accurate result, clean both the tape and the part before measuring and use the specified measuring tension.

 

Inch Pi Tapes

Pi Tape inch Vernier scale example

The standard gage member is 1/4" wide. Optional 1/8", 3/8" and 1/2" widths are available for certain applications.

The Vernier scale divides each graduation on the tape body into 25 parts, allowing readings to .001 inch.

Example: if the divisions to the left of the Vernier zero indicate 20.025 inches and the 15th Vernier line coincides with a line on the gage member, the reading is 20.040 inches.

When reading a standard O.D. tape, apply a snug pull of approximately 5 lb. tension after properly cleaning the tape and part.

Metric Pi Tapes

Pi Tape inch Vernier scale example

The standard metric gage member is 6.35 mm wide. Optional 4.76, 9.53 and 12.70 mm widths are available for certain applications.

Each line on the gage member represents 0.5 mm of diameter, while each line on the Vernier represents 0.01 mm. For example, if the Vernier zero is past the 661.5 mm line and the 23rd Vernier line coincides, the diameter reading is 661.73 mm.

When reading the metric O.D. tape, apply a snug pull of approximately 2.25 kg tension after properly cleaning the tape and part.

Important: Measuring technique affects accuracy. Keep the tape straight, parallel to the part and under the manufacturer's specified tension. A damaged, kinked or improperly tensioned tape can produce an inaccurate reading.
 

Measuring Inside Diameter with an Outside Diameter Tape

A standard O.D. Pi Tape can be used for certain inside-diameter measurements by accounting for the tape thickness and using zero tension. However, for the most accurate direct inside-diameter measurement, a dedicated Pi Tape Inside Diameter or O-Ring Tape is recommended.

For a standard metric O.D. tape, the current published procedure specifies adding twice the tape thickness to the reading. Standard tapes are 0.25 mm thick, so 0.50 mm is added when using the standard O.D. tape for this type of I.D. measurement.

For large diameters, small pieces of masking tape can be used to help hold the Pi Tape parallel to the component while taking the measurement.

 

Pi Tape Care and Storage

  • Wipe the tape clean after use.
  • Apply a light rust-preventive oil before storage when appropriate.
  • Store the tape in its protective container.
  • No periodic adjustment is normally required.
  • Do not step on, kink, dent or sharply bend the tape.
  • Damage to the tape can affect measurement accuracy.
 
 
 

Specialty Pi Tapes

Pi Tape® specialty products are available for applications that cannot be handled by a standard outside diameter tape.

Special Pi Tapes

Easy-read, stainless steel, inside diameter, narrow or wider width, special thickness, Go/No-Go inspection, extra-capacity and intermediate-range Pi Tapes.

Inside Diameter & O-Ring Tapes

Precision tapes specifically designed for quick and accurate inside diameter measurement of O-rings and other soft-walled parts.

Custom and special Pi Tapes can be manufactured to suit particular measuring requirements. Contact Newman Tools if you need a diameter range, width, thickness, material or inspection configuration that is not listed here.

 
 

Pi Tape® Frequently Asked Questions

What is a Pi Tape used for?
- A Pi Tape is used to measure the diameter of round or cylindrical parts by measuring their circumference and providing a direct diameter reading.

What sizes of Pi Tape are available?
- Standard Pi Tapes are available in a wide range of inch and metric diameter sizes, from small diameters through very large industrial applications. Extra-large tapes are available by special order.

What is the PI-1 Pi Tape?
The PI-1 is a standard inch Pi Tape covering a 2 to 12 inch outside diameter range.

Are metric Pi Tapes available?
Yes. Metric Pi Tapes are available in a range of sizes from 28–200 mm through 3300–3600 mm, with additional large-diameter sizes available by special order.

Can a Pi Tape measure inside diameter?
A standard O.D. tape can be used for certain I.D. measurements by applying the appropriate correction, but a dedicated inside-diameter Pi Tape is recommended when direct I.D. accuracy is required.

Are stainless steel Pi Tapes available?
Yes. Stainless steel Pi Tapes are available for applications where corrosion resistance is important. Material and size limitations should be confirmed for the specific tape required.

Where can I buy Pi Tapes?
Newman Tools supplies Pi Tape® precision diameter measuring tapes in Canada, the USA and worldwide. See our Pi Tape price list or contact us for assistance selecting the correct size.
 

Pi Tapes from Newman Tools

Newman Tools has supplied high-quality tools and supplies to machine shops, plant engineering and maintenance since 1955. We supply Pi Tape® precision diameter measuring tapes in inch and metric sizes and can assist with standard, large-diameter and specialty applications.

We ship worldwide, including Canada and the USA. For current pricing or help selecting a Pi Tape, please contact Newman Tools.

 

 

Trademarks are the properties of their respective owner(s).

Oct 2026, July 2024, Oct 2023, March 2021, 2020, April 2019, June 2016, November 2010, October 2009

The descriptions, illustrations, specifications, dimensions, and part numbers are subject to change without notice.


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