Free heating oil tool · Updated 5 August 2026

Oil Tank Dip Chart: Convert Your Dipstick Reading to Litres

A dip stick shows the oil depth, not the litres. On a 999 litre 1,000 litre, a reading of 40cm is about 339 litres, or 34% full. Filling to the 85% safe level of 849 litres would cost about £495 at 92.5p per litre on 5 August 2026.

Your reading

Tank make or size

Units

Dip reading, oil depth from the bottom (cm)

Typical daily usage (litres)

Price per litre (pence)

Today's UK average 92.5p per litre on 5 August 2026. Change it above.

What you have

Oil remaining

339litres

About 34% full of a 999 litre tank.

Days of heating left

28 days

At your stated daily usage.

Cost to fill to safe fill

£495

About 510 litres to reach 85% at 92.5p per litre.

A worked example

Say you dip a 1,000 litre oil tank and the wet mark sits at 40cm. That tank holds about 999 litres full and stands 118cm tall inside, so 40cm of depth is roughly 339 litres, or 34% full.

To top up to the 85% safe fill of about 849 litres you would order roughly 510 litres. At today’s UK average of 92.5p per litre on 5 August 2026, that comes to about £495 including VAT.

Full dip chart: 1,000 litre oil tank

Every 5cm of depth, computed for a 999 litre tank. Common makes: Harlequin 1000ITT, Deso V1000, Titan EcoSafe 1000.

Depth (cm)	Litres	% full
5	42	4%
10	85	8%
15	127	13%
20	169	17%
25	212	21%
30	254	25%
35	296	30%
40	339	34%
45	381	38%
50	423	42%
55	465	47%
60	508	51%
65	550	55%
70	592	59%
75	635	64%
80	677	68%
85	719	72%
90	762	76%
95	804	81%
100	846	85%
105	889	89%
110	931	93%
115	973	97%
118	999	100%

Need another size? We publish full printable dip charts for the 1,000 litre, 1,200 litre, 1,360 litre and 2,500 litre tanks.

How this is calculated

Read the oil depth from the bottom of the tank with a clean dip stick.

Rectangular / upright tank (linear with depth):
  litres = capacity x (depth / full_height)

Horizontal cylinder (circular segment, non-linear):
  segment_area = r^2 x acos((r - h) / r) - (r - h) x sqrt(2 x r x h - h^2)
  litres       = segment_area x length / 1000

safe_fill = capacity x 0.85   (tank_safe_fill_pct, verified 2026-07-28)
cost_to_fill = (safe_fill - litres) x ppl / 100 x (1 + VAT)

Worked example (1,000 litre oil tank, depth 40cm):
  capacity = 999 litres, litres at 40cm = 339 (34% full)
  fill to 849 litres costs ~£495 at 92.5p/L

Figures used on this page

Figure	Value	Source	Verified
tank safe fill pct	0.85 ratio	OFTEC guidance: tanks are filled to 80-90% of stated capacity to allow expansion	2026-07-28
vat domestic	0.05 ratio	VAT Act 1994 Schedule 7A Group 1, domestic fuel reduced rate	2026-07-28

What affects the result

Tank shape. Upright and rectangular tanks fill roughly in line with depth. A lying-down cylinder does not: the same 5cm near the bottom holds far less oil than 5cm across the middle, so a shape-specific chart matters.

Where the outlet sits. The boiler feed usually sits a little above the very bottom, so the last few centimetres of the chart may not be usable oil. Do not run the tank right down to zero.

Sludge and water. Older tanks collect sludge and condensation at the base. A dip reading near the bottom can include material you would not want drawn into the boiler, so treat low readings with caution.

Reading technique. Keep the rod vertical and let it rest on the base. A tilt in the rod or a tank sitting slightly off level will shift the wet mark and change the litres you read off the chart.

Oil Tank Dip Chart FAQs

How do I read an oil tank dip stick?

Wipe a clean rod, lower it straight down until it touches the bottom, then read the wet mark. That length is the oil depth. Match it to the row for your tank in the chart on this page to convert the depth into litres.

Why does a dip reading not equal a percentage full?

For a lying-down cylinder the tank is narrow near the bottom and top, so depth and litres are not proportional. Only upright and rectangular tanks fill roughly in line with depth. Always use a chart matched to your tank shape.

Which tanks does this cover?

The charts cover common UK makes including Harlequin, Titan, Deso, Carbery, Kingspan and Balmoral, with dedicated pages for 1,000, 1,200, 1,360 and 2,500 litre tanks. For anything else, enter your own dimensions in the calculator to build a custom chart.

How many litres is my tank when full?

The example 1,000 litre oil tank holds about 999 litres. In practice you fill to around 85% of that, roughly 849 litres, to leave room for expansion and avoid overfilling at delivery.

Can I print the dip chart?

Yes. The tables on this page and on each preset page are plain HTML, so they print cleanly. Many people tape a printed chart to the inside of the tank lid or the garage wall next to the dip stick.

How accurate is a dip reading?

Treat it as a good guide, not a precise gauge. A slight tilt in the tank, sludge at the bottom or a bent rod all move the figure a little. For ordering decisions the reading is easily accurate enough.