# Converting From Linear Flow (cm/hour) to Volumetric Flow Rates (mL/min) and Vice Versa

It is convenient when comparing results for columns of different sizes to express ﬂow as linear ﬂow (cm/hour). However, ﬂow is usually measured in volumetric ﬂow rate (mL/min).

To convert between linear ﬂow and volumetric ﬂow rate use one of the formulae below.

**From linear ﬂow (cm/hour) to volumetric ﬂow rate (mL/min)**

Volumetric ﬂow rate (ml/min) = | Linear ﬂow (cm/h) 60 |
x column cross sectional area (cm^{2}) |

= | Y 60 |
× | π x d 4 |

where

Y = linear flow in cm/h

d = column inner diameter in cm

*Example*:

What is the volumetric flow rate in an XK 16/70 column (i.d. 1.6 cm) when the linear flow is 150 cm/hour?

Y = linear flow = 150 cm/h

d = inner diameter of the column = 1.6 cm

Volumetric ﬂow rate (ml/min) = | 150 × π × 1.6 x 1.6 60 × 4 |
mL/min |

= 5.03 ml/min

**From volumetric flow rate (mL/min) to linear flow (cm/hour)
**

Linear ﬂow rate = | Volumetric ﬂow rate (ml/min) × 60 column cross sectional area (cm ^{2}) |

= Z × 60 × | 4 π x d |

Z = volumetric flow rate in mL/min

d = column inner diameter in cm

*Example*:

What is the linear flow in an HR 5/5 column (i.d. 0.5 cm) when the volumetric flow rate is 1 mL/min?

Z = Volumetric flow rate = 1 mL/min

d = column inner diameter = 0.5 cm

Linear ﬂow = 1 × 60 × | 4 π x 0.5 x 0.5 |
cm/h |

= 305.6 cm/h

**From mL/min to using a syringe**

1 mL/min = approximately 30 drops/min on a HiTrap 1 mL column

5 mL/min = approximately 120 drops/min on a HiTrap 5 mL column

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