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What Is A Strapping Chart?

tank level measurementWhen volume is a concern, your tank might just come with a strapping chart. This chart tells you what volume you have at what levels. For example, at 5 inches, you may have 5 gallons, and at 8.5 inches, you might have 10 gallons.

Another name for a strapping chart is a calibration table. It’s an invaluable tool for ensuring your level measurements are accurate.

Non-linear tanks need strapping charts to identify volumes because it cannot be calculated with simple equations. These tanks are sometimes calibrated either by the manufacturer or a professional service to ensure an accurate volume can be calculated at important intervals.

Common Strapping Chart Features

INCHES MM BBL LITERS US GAL
6.97 177 1 159 42
9.96 253 2 318 84
12.56 319 3 477 126
15.08 383 4 636 168
17.64 448 5 795 210
The essential information in a strapping chart is primarily a height, or level, measurement paired with a volume, be it in gallons, barrels, liters, etc. The purpose is to convert a linear level measurement to a volume – often a more useful measurement.

5 ft of liquid in a small process tank is very different than 5 ft of liquid in a large terminal tank.

The resolution of the increments can vary. Some measure every inch; others may use feet. Volume is often the primary increment; an oil tank might only show a measurement for every barrel (42 US gallons).

A combination of units of measurement is common. For example, you’ll often see levels measured in both inches and millimeters, and volume in gallons and liters.

Why Is It Called A “Strapping Chart”?

The term comes from calibrating a tank by measuring it with a steel tape, or strap. Modern day tank calibration instruments include high tech tools such as laser levels and ultrasonic thickness gauges, but the practice has humble beginnings.

So tank strapping is tank calibration, and the strapping chart is the output.

Other Terms For Strapping Chart

There are several other terms used that mean the same thing. These include:

  • Strapping Table
  • Calibration Table
  • Tank Chart
  • Tank Calibration Chart
  • Tank Gauge Chart
  • Gauge Table
  • Dip Charts

You get the idea. These names all refer to a table, or chart, for converting a linear level into a volume. The common term may change a bit based on industry and location. However, the most common term as far as we can tell is strapping chart.

How To Use A Strapping Chart

This may seem obvious, but you use a strapping chart by comparing level measurements to convert to a volume. However, with modern day level sensors, either the sensor or the control system does this for you – unless the tank isn’t linear.

Several APG level sensors allow you to put the strapping chart directly into the sensor via Modbus programming software. These include the MPX magnetostrictive level transmitter and the MNU ultrasonic level sensors.

It’s also a good idea to use the strapping chart on occasion to check the accuracy of your sensor. This will help you make necessary adjustments, or even find a new sensor if needed.

If you have any questions about how to use your level sensor and strapping chart together for a better level measurement, let us know - we’re happy to help!


Extremely accurate and simple. What else are you looking for? Check out our float level transmitters today:

top image credit: U.S. Department of Agriculture via flickr cc

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