# Tanker unloading calculator

> A free calculator for a tanker's delivery into one underground tank: litres from the dip before and after, plus sales during unloading, compared with the invoice litres.

Canonical: https://dipdensity.watsinfo.com/tools/tanker-unloading-calculator/
Last updated: 2026-11-02

**Short answer:** Choose the tank, type the dip before and after unloading, the litres sold from that tank meanwhile, and the invoice litres. Received is the litres after, less the litres before, plus the litres sold. The gap against the invoice is your shortage or excess.

The calculator runs in the browser at https://dipdensity.watsinfo.com/tools/tanker-unloading-calculator/.

## The sum

```
received = litres at the dip after − litres at the dip before + litres sold meanwhile
gap      = received − invoice litres
```

The litres at each dip come from the tank model's chart, the same as the [dip to litres calculator](https://dipdensity.watsinfo.com/tools/dip-to-litres-calculator/).

## Take the dips properly

- Take the **dip before** once sales from the tank have stopped, just before decanting starts.
- Let the fuel settle after unloading. Take the **dip after** once the surface is still, usually 10 to 15 minutes.
- Use the same rod both times, and read the cut at eye level.

## If it comes out short

Check the dips first. A bar misread on the rod is often 20 to 30 litres in a 20 KL tank. If the shortage stands, see [what to do about a tanker shortage](https://dipdensity.watsinfo.com/guides/tanker-shortage/).

## Questions

### Why add the litres sold during unloading?

The MDG asks you to stop sales from the tank being filled until decanting ends. If any were sold anyway, they left the tank while fuel came in, so the dip after is that much lower than it should be.

### A few litres short. Is that a problem?

Not always. The invoice states litres at the depot's temperature, and your dips are at the tank's temperature. A few litres either way is normal. A steady shortage load after load is worth raising.

### Where should a shortage be caught?

In the tank lorry, before decanting. The MDG asks you to dip every compartment against its calibration certificate. A short dip there is made up from the lorry's own product and written on the invoice.

## Sources

- [BPCL, Marketing Discipline Guidelines 2024](https://www.bharatpetroleum.in/images/files/MDG-2024-Effective-24-10-2024.pdf)