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Homeowner's guide to:

Oil Central Heating

Oil Tank Gauge

How Do I Read An Oil Tank Chart?

Your fuel oil tank probably came with a float-style oil tank gauge. This gauge has a float attached to a hinge that indicates the level of oil in the tank. There is a disk at the end of the float that lowers with it. Refer to the diagram below for a visualization of how this happens.


A typical heating oil tank features a float gauge with a hinged arm. As the float lowers, the visible disk on the top of the heating oil tank moves down accordingly.

To read the level of a float gauge, look for the tick marks on the plastic vial. These typically indicate Full, 3/4, 1/2, and 1/4. Because the home heating oil tank is rounded at the bottom, these gauges are not very accurate when the tank is low. As a good rule of thumb, always order heating oil online at around 1/4 full. This gives you a few days for the oil to arrive before running out.

To read the oil tank gauge, refer to the tick marks on the side. On most models, these are 1/4, 1/2, 3/4, and Full. The shape of heating oil tanks means that the oil tank chart is less accurate at lower ranges. As a result, most experts recommend to order more oil at 1/4 full. This gives you leeway and avoids you ever running out of oil.

To approximate how much heating oil you have left in your tank, multiply the oil tank gauge reading by the size of your tank. For example, if your gauge is around 3/4 and your tank is 275 gallons, you have approximately 3/4 * 275 = 207 gallons.

How Accurate is My Oil Tank Chart?

Usually, your oil tank gauge is not very precise and should only be used as a guiding approximation of the oil left in your tank. Its design is also prone to wear and tear, which means it can break down. If your gauge hasn’t moved in a while, it could be stuck. Unscrew the plastic vial and press the disk down – if it doesn’t move down easily and then float back up, there could be an issue with it.

A heating oil tank gauge can get stuck by rotating inside the fuel oil tank. In this case, the float becomes wedged against the side of the tank and cannot move.

The float on the oil tank gauge could also become less buoyant, by developing sludge that weighs it down and doesn’t let it float on top of the oil. This is another reason why cleaning your oil tank is a good idea.