Pumps characteristic curves are often in head - feet or metres - and a conversion to pressure scales commonly used in pressure gauges - like psi or bar - may be required.

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### Converting Head to Pressure

Converting head in*feet*to pressure in

*psi*

Pumps characteristic curves in feet of head can be converted to pressure - psi - by the expression:

*p = 0.433 h SG (1)*

*where*

*p = pressure (psi)*

*h = head (ft)*

*SG = specific gravity of the fluid*

*metre*to pressure in bar

Pumps characteristic curves in metre of head can be converted to pressure - bar - by the expression:

*p = 0.0981 h SG (2)*

*where*

*h = head (m)*

*p = pressure (bar)*

*metre*to pressure in kg/cm2

Pumps characteristic curves in *metre* of head can be converted to pressure - kg/cm2 - by the expression:

*p = 0.1 h SG (2b)*

*where*

*h = head (m)*

*p = pressure (*kg/cm2*)*

### Converting Pressure to Head

Since pressure gauges often are calibrated in pressure - psi or bar - a conversion to the heads commonly used in pump curves - like *f*eet or meter - may be required.

*psi*to head in feet

*h = 2.31 p / SG (3)*

*where*

*h = head (ft)*

*p = pressure (psi)*

*bar*to head in metre

*h = p 10.197 / SG (4)*

*where*

*h = head (m)*

*p = pressure (bar)*

*h = p 10 / SG (4b) *

*where*

*h = head (m)*

*p = pressure (kg/cm2)*

### Example - Converting Pump Head - feet - to Pressure - psi

The pressure - psi - of a water pump operating with head 120 ft can be calculated with eq. 1 as:

*p = 0.433 (120 ft) (1) *

* = 52 psi*

### Example - Converting Pressure - psi - to Pump Head - feet

The head in*feet* water column can be calculated from pressure *100 psi *with eq. 3 as:

*h = 2.31 (100 psi) / (1)*

*= 231 ft*

Where specific gravity of water = *1*.

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### Feet of Head Water to psi

Head*(ft)*Pressure

*(psi)*

1 | 0.43 |

2 | 0.87 |

3 | 1.30 |

4 | 1.73 |

5 | 2.17 |

6 | 2.60 |

7 | 3.03 |

8 | 3.46 |

9 | 3.90 |

10 | 4.33 |

20 | 8.66 |

30 | 13.0 |

40 | 17.3 |

50 | 21.7 |

60 | 26.0 |

70 | 30.3 |

80 | 34.7 |

90 | 39.0 |

100 | 43.3 |

120 | 52.0 |

140 | 60.6 |

160 | 69.3 |

180 | 78.0 |

200 | 86.6 |

250 | 108 |

300 | 130 |

350 | 152 |

400 | 173 |

500 | 217 |

600 | 260 |

700 | 303 |

800 | 346 |

900 | 390 |

1000 | 433 |

*62°F (17°C)*

Download pressure vs head imperial units as pdf file

Download water pressure vs head - SI units as pdf file

### Head vs. Pressure when handling Liquids of different Density

LiquidSpecific GravityHead*(ft)*Pressure

*(psi)*

Water | 1.0 | 100 | 43.3 |

Kerosene | 0.8 | 100 | 36.6 |

Sulphuric Acid | 1.8 | 100 | 77.9 |

Identical pumps will develop the same head when running at the same speed but the discharge pressure is quite different due to the different densities of the liquids. It can be simpler to discuss the performance pumps in terms of head rather than pressure since the use of head makes the pump curve applicable to any liquid regardless of density.