Flow Measurement · Glossary

What is Beta Ratio?

Symbol: βdimensionlessFlow Measurement

Beta ratio is the bore diameter of an orifice, nozzle or venturi throat divided by the pipe internal diameter.

Beta Ratio Explained

Beta ratio sets how much a DP flow element restricts the pipe. A small beta gives a high DP for a given flow; a large beta gives a low DP and lower pressure loss.

ISO 5167 gives valid beta ranges for each element. Beta also sets the straight pipe lengths needed: higher beta needs longer upstream runs.

Beta Ratio Formula

β = d ÷ D

d	orifice bore or throat diameter at operating temperature
D	pipe internal diameter at operating temperature

Example: A 50 mm bore in a 100 mm pipe gives β = 0.5.

Beta Ratio: Typical Values

Orifice plate (ISO 5167-2)	0.10 to 0.75
Typical design choice	about 0.4 to 0.7

Calculators for Beta Ratio

CalculatorOrifice Bore CalculatorFree online calculator with formula and worked example.CalculatorOrifice Flow CalculatorFree online calculator with formula and worked example.CalculatorStraight Pipe Run CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadFlow Measurement Formulas Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Beta Ratio?

Beta ratio is the bore diameter of an orifice, nozzle or venturi throat divided by the pipe internal diameter.

What beta ratio is best for an orifice?

Usually between about 0.4 and 0.7: high enough to limit pressure loss, low enough to keep straight run lengths and uncertainty reasonable.

Does beta change with temperature?

Slightly. Bore and pipe expand differently, so ISO 5167 uses diameters at operating temperature.

Learn more on the blog

Mistakes in DP flow measurement

A practical guide on instrumentationblog.in with more detail on beta ratio and how it is applied on real plants.

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More Flow Measurement Terms

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