Tru-Trac® & Measuring Wheel Calculators

With the Tru-Trac® family of products, EPC has simplified linear measurement with an integrated rotary encoder and measuring wheel. You can also customize your linear solution with the various accessory brackets and wheel options EPC offers.

In order to use EPC products with ease in your application, below are calculators to help you tailor your product selection. Uncertain what encoder CPR is needed to meet a control system’s specified or desired requirements? Or given a known CPR and resolution, what is the appropriate measuring wheel? Use these tools to narrow your selections.

Linear resolution

Linear resolution (RES) is the smallest increment of measurement required by the application. For example, if your material needs to be measured and cut down to 1/4", your required linear resolution is 0.25".

Linear resolution (RES) is typically specified in cut-to-length applications such as lumber mills, textiles, spooled cable, or rolled paper. In these applications, an encoder-measuring wheel assembly measures the distance travelled via contact with the material itself or the conveyor surface.

Pulses per unit of measurement

In applications where linear distance travelled is measured in pulses, pulses per unit of measurement (PPU) is another way to specify linear resolution. Typically a minimum number of encoder pulses per millimeter or inch is a documented design or system requirement.

This is common in applications such as printing, scanning, and x-y positioning, where devices are looking for a minimum specific number of pulses as an object travels through the system.

Convert between RES and PPU

To convert linear resolution (RES) to pulses per unit (PPU), or vice-versa, calculate as follows. Specify your unit of measurement (UOM).




CIRC = circumference of wheel OR linear distance travelled in one revolution
RES = linear resolution in unit of measurement
PPU = pulses per unit of measurement
CPR = counts per revolution (encoder resolution)
UOM = unit of measurement (1 in, 1 mm, 1 ft, etc.)

NOTE: CIRC, RES and UOM must use the same unit (inches, feet, millimeters). 1 inch = 25.4 mm.

Solve for encoder resolution, wheel circumference, or linear resolution

IMPORTANT: Enter values into any two fields to solve for the third. Leave the blank value blank. Do not enter 0 or any spaces.

NOTE: CIRC, RES and UOM must use the same unit (inches, feet, millimeters). 1 inch = 25.4 mm.

Convert inches to mm: inches * 25.4 = mm

Convert mm to inches: mm / 25.4 = inches


1. Solve for CPR, CIRC, or RES

Example: "I want to measure down to 0.01 inches (RES). I have a 12" circumference wheel (CIRC). What encoder resolution (CPR) do I need?"


2. Solve for CPR, CIRC, or PPU

Example: "My printer/controller requires 22 pulses/mm (PPU). My encoder's resolution (CPR) is 6600. What size measuring wheel do I need?"

Related products & documentation


EPC offers all-in-one and customizable linear measurement solutions. Our Tru-Trac® series of an integrated encoder, bracket, and measuring wheel are compact, simplify your system design, and reduce overall cost. For wheeled absolute or programmable linear measurement, our Model PLMS can be customized by choosing an encoder, output type or protocol, measuring wheel and mounting bracket. Visit Linear Measurement Accessories to compare measuring wheel and mounting bracket options.

Need linear measurement without a wheel? See our Model LCX Draw Wire series for a wide range of options.


For more information, read the technical bulletin TB-108 Encoders with Measuring Wheels.

CPR, RPM, Frequency Calculator

Use our related CPR, RPM, Frequency Calculator to help specify your incremental encoder.


More Resources

As the term implies, rotary encoders generally provide feedback for rotary motion. However, with the addition of a measuring wheel, gear, or cable-draw assembly, a rotary encoder can also provide feedback for linear displacement or measurement. EPC offers a line of integrated linear measurement solutions. They’re easy to install and deliver reliable, accurate feedback for applications such as cut-to-length, spooling, length measurement and print registration. For more information on choosing the right measuring wheel for your application, refer to Technical Bulletin TB-108: Encoders with Measuring Wheels.


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