Why density is checked at 15 °C
Petrol and diesel expand as they get warmer, so the same fuel reads lighter on a hot afternoon than on a cool morning. To compare a reading taken at the pump with the density printed on the challan, both have to be at the same reference temperature. In India, as in most of the world, that reference is 15 °C.
A density at 15 °C that is noticeably different from the challan can mean the product has been mixed, adulterated or swapped in transit. That is why the density check is done before a tanker is decanted and recorded in the density register.
The method used
This calculator uses the ASTM D1250 / API Table 53B (generalized products) method, which is what the printed density conversion charts at Indian pumps are based on. It finds the thermal expansion of the product from its density, works out the volume correction for the temperature difference from 15 °C, and corrects for the expansion of the glass hydrometer.
- Petrol falls in the gasoline band of the table, diesel in the fuel-oil band. The calculator picks the band automatically.
- Results are shown to one decimal place in kg/m³.
- Small differences of a few tenths from a printed chart are normal, because charts are rounded.
Comparing with the challan
Enter the challan density to see the difference. Oil companies allow a small tolerance between the challan density and the density you measure, commonly ±3 kg/m³. Check the exact limit in your oil company's current guidelines. If the difference is outside the limit, do not decant: record it and inform your oil company's sales officer.
Frequently asked questions
What is the normal density of petrol and diesel in India?
Specifications allow a range, and each load's density at 15 °C is printed on its challan. Petrol is typically somewhere around 720–775 kg/m³ and diesel around 820–860 kg/m³. What matters at the pump is not the range but whether your reading matches the challan.
My hydrometer reads in g/ml. What do I enter?
Multiply by 1000. A reading of 0.742 g/ml is 742 kg/m³.
Is this the same as the ASTM 53B table?
Yes, it uses the Table 53B equations instead of the printed lookup, so it works for any reading rather than only the rows in a chart.