what is my measurement device showing?

Spindle hydrometers (Araoemeters)

Either show „density” OR „specific/relative Density“ ! Most devices available in Europe show „density“, whereas devices from USA mostly show „specific/relative density“.

pointer hydrometers

Nearly always show „specific/relative Density“.

Indications for devices showing “density” :

  • Imprint: „Density“ OR „Dichte“
  • Imprint of measured unit in [g/cm³]
  • Imprint „25/4°C“ or „25°C“ (or equivalent in °F) This devices apply their measurement value to water at 4°C / 39°F, which has a density of 1.000.

Indications for devices showing “specific/relative density”:

  • Imprint : „specific density“ or “specific gravity” or „SG“
  • No imprint of measured unit : e.g. [-]/N.a.
  • Imprint „25/25°C“

Measurement value is relative to water at 25°C / 77°F, which has a density of 0.997. Value displayed is density divided by 0.997 and thus higher than the „normal density “ Tip: Related temperature can also be different to 25°C/77°F. In this case you have a calibration different to 25°C/77°F

change your Aqua-Calculators preferences accordingly!

In case you are still unsure about your device, contact the manufacturer!


Refractometers: They measure „salinity“ but nearly always also show also the “relative density” on a second scale. Recommendation: Use salinity scale only!