ABV & Hydrometer Corrections Add your OG and FG to work out ABV. Leave calibration temp at 20 °C if your hydrometer is new; older models may be calibrated at 15 °C. Hydrometer OG 1.05 SG Hydrometer FG 1.01 SG Temperature OG 20 °C Temperature FG 20 °C Calibration Temp 20 °C