How to Calculate Petrol Pump DIP Stock from the Calibration Chart

What is a DIP reading?

A DIP reading is the height of fuel in an underground tank, measured with a graduated dip rod lowered to the bottom of the tank. It is usually read in centimetres or millimetres. Because tanks are cylinders lying on their side, the height does not convert to litres in a straight line — that is what the calibration chart is for.

What is the calibration (DIP) chart?

Every tank comes with a calibration chart that lists, for each DIP height, the volume of fuel in litres. Charts are specific to the tank: two 20 KL tanks of different make can have different charts. Always use the chart for that tank.

Step 1: Take the DIP correctly

• Take the DIP at the same time every day, ideally before the first shift starts.
• Wait for the fuel to settle if a tanker has just been decanted.
• Lower the rod vertically until it touches the bottom, then lift and read the wet mark.
• Note the reading in the same unit as the chart (cm or mm).

Step 2: Look up the volume

Find the DIP height in the chart and read the volume. If the exact height is not listed, use the volume for the nearest listed height, or interpolate between the two nearest rows: volume = lower volume + (DIP − lower DIP) × (upper volume − lower volume) ÷ (upper DIP − lower DIP).

Example (illustrative values): the chart shows 150.0 cm = 11,180 L and 151.0 cm = 11,260 L. A DIP of 150.5 cm gives 11,180 + 0.5 × 80 = 11,220 L.

Step 3: Work out book stock

Book stock = previous DIP stock + receipts since then − sales since then. Receipts are the litres decanted from tankers; sales are the litres from approved DU sheets for the nozzles on that tank.

Step 4: Compare DIP stock with book stock

Variation = DIP stock − book stock. A small variation is normal because of temperature and reading accuracy. A variation that keeps growing in one direction needs attention.

• Consistent loss – possible leak, meter giving more than it shows, or theft.
• Sudden loss after a receipt – short delivery from the tanker; check the DIP before and after decantation.
• Gain – a meter giving less than it shows, a receipt entered twice, or a DIP reading error.
• Water – check water in the tank with water-finding paste; water raises the DIP without adding fuel.

Keep a daily record

Record DIP, receipts, sales and variation for each tank every day. A one-off variation tells you little; a trend over a week or a month tells you a lot.

Let the app do the lookup

In Petronix DIP and tank stock, you upload each tank’s calibration chart once. Staff enter the DIP in cm or mm on the phone, the app finds the litres from the chart, and book stock is updated automatically from purchases and approved DU sheets, so the variation is visible the same day.