Specific gravity is a comparison ratio between the density of a particular substance and the density of a reference substance. Since the density of the reference substance will vary depending on its temperature, the specific gravity should also include the temperature of the reference media.

A very common reference media used for the calculation of specific gravity is fresh water at 4 degrees Celsius, which is very close to the temperature at which water is most dense.

The main use of specific gravity in pressure measurement is to calibrate hydrostatic liquid level measurement equipment. The majority of hydrostatic pressure measurement devices are calibrated in depth of water units such as mH2O or ftWG. Therefore if you want to use these devices to measure the level of a liquid which has a lower specific gravity than water, such as oil for example, you will need to re-calibrate the range from metres of water to meters of oil. The easiest way to do this is to divide the range in meters of water by the SG of the oil.

The calculation of specific gravity is very important to the management of liquid storage tanks, where the quantity of liquid contents has to be determined precisely for commercial purposes.

**Hydrostatic pressure measurement products**

- LMP305 Borehole Level Transmitter
- DPT200 Pressurised Tank Level Differential Pressure Transmitter
- LMP307 Submersible Level Transmitter
- LMK382 Low Range IP68 Waste Water Level Transmitter

## Measurement Unit Related Terms

More pages related to measurement unit technical terms.

- at – Technical Atmosphere Pressure Unit
- atm – Standard Atmosphere Pressure Unit
- bar Pressure Unit
- cmH2O – Centimetres of Water Column at 4 deg C Pressure Unit
- cmHg – Centimetres of Mercury at 0 deg C Pressure Unit
- daPa – Dekapascal Pressure Unit
- dyn/cm² – Dyne per Square Centimetre Pressure Unit
- ftH2O – Feet of Water Column at 4 deg C Pressure Unit
- g – Acceleration due to Gravity
- g/cm² – Grams per Square Centimetre Pressure Unit
- hPa – Hectopascal Pressure Unit
- inH2O – Inches of Water Column at 4 deg C Pressure Unit
- inHg – Inches of Mercury at 0 degrees C Pressure Unit
- kg/cm² – Kilogram per Square Centimetre Pressure Unit
- kg/mm² – Kilogram per Square Millimetre Pressure Unit
- kPa – Kilopascal Pressure Unit
- ksi – Kilopounds per Square Inch Pressure Unit
- mbar – Millibar Pressure Unit
- mH2O – Metres of Water Gauge at 4 deg C Pressure Unit
- mmH2O – Millimetres of Water Column at 4 deg C Pressure Unit
- mmHg – Millimetres of Mercury at 0 deg C Pressure Unit
- MPa – Megapascal Pressure Unit
- mPa – Millipascal Pressure Unit
- mTorr – Millitorr Pressure Unit
- N/cm² – Newton per Square Centimetre Pressure Unit
- N/m2 – Newton per Square Metre Pressure Unit
- N/mm² – Newton per Square Millimetre Pressure Unit
- oz/in² – Ounce per Square Inch Pressure Unit
- Pa – Pascal Pressure Unit
- Pressure
- Pressure Units
- psf – Pounds per Square Foot Pressure Unit
- psi – Pounds per Square Inch Pressure Unit
- Torr Pressure Unit
- tsf – Tons per Square Foot (USA, Short) Pressure Unit
- tsi – Tons per Square Inch (UK, Long) Pressure Unit
- tsi – Tons per Square Inch (USA, Short) Pressure Unit
- Water Density
- µHg – Micron of Mercury at 0 deg C Pressure Unit