Transformer Oil Capacity Chart: kVA to Liters/Gallons (5-2500 kVA) [2026]

If you're looking for a quick answer to "how much oil is in my transformer," you've come to the right place. However, as any experienced engineer in our factory will tell you: there is no single universal number. The oil capacity depends heavily on the voltage class, cooling type (ONAN/ONAF), and tank design (corrugated fins vs. radiators).

 

 

Below is a general reference chart based on typical 11kV/400V ONAN oil-immersed distribution transformers. We use these figures as standard estimates for logistics, maintenance planning, and oil filtration services.

 

 

⚠️ Factory Note: These values are approximations based on standard industrial designs. Always check the nameplate on your specific unit for the exact volume required for your transformer.

 

Single-Phase Transformers (Pole Mounted – Round Tank)

kVA Rating	Oil Volume (Liters)	Oil Volume (Gallons)	Approx. Oil Weight (kg)*
5 kVA	15 – 20 L	4 – 5 gal	13 – 18 kg
10 kVA	25 – 30 L	6 – 8 gal	22 – 27 kg
15 kVA	40 – 55 L	10 – 15 gal	35 – 49 kg
25 kVA	60 – 80 L	16 – 21 gal	53 – 71 kg
37.5 kVA	80 – 100 L	21 – 26 gal	71 – 89 kg
50 kVA	100 – 130 L	26 – 34 gal	89 – 116 kg
75 kVA	140 – 170 L	37 – 45 gal	125 – 151 kg
100 kVA	180 – 210 L	48 – 55 gal	160 – 187 kg
167 kVA	250 – 300 L	66 – 79 gal	223 – 267 kg

 

Three-Phase Transformers (Distribution & Power – Rectangular/Fin Tank)

kVA Rating	Oil Volume (Liters)	Oil Volume (Gallons)	Approx. Oil Weight (kg)*
15 kVA	60 – 80 L	16 – 21 gal	53 – 71 kg
30 kVA	90 – 110 L	24 – 29 gal	80 – 98 kg
45 kVA	110 – 140 L	29 – 37 gal	98 – 125 kg
75 kVA	160 – 190 L	42 – 50 gal	142 – 169 kg
100 kVA	200 – 250 L	53 – 66 gal	178 – 223 kg
150 / 160 kVA	280 – 340 L	74 – 90 gal	250 – 302 kg
200 kVA	350 – 420 L	92 – 111 gal	311 – 374 kg
315 kVA	480 – 550 L	127 – 145 gal	427 – 490 kg
500 kVA	650 – 800 L	172 – 211 gal	579 – 712 kg
630 kVA	800 – 950 L	211 – 251 gal	712 – 846 kg
800 kVA	1,000 – 1,200 L	264 – 317 gal	890 – 1,068 kg
1,000 kVA	1,200 – 1,500 L	317 – 396 gal	1,068 – 1,335 kg
1,500 / 1,600 kVA	1,600 – 2,000 L	423 – 528 gal	1,424 – 1,780 kg
2,000 kVA	2,100 – 2,600 L	555 – 687 gal	1,869 – 2,314 kg
2,500 kVA	2,600 – 3,200 L	687 – 845 gal	2,314 – 2,848 kg

*Oil weight is calculated based on a typical mineral transformer oil density of 0.89 kg/L at 20°C.

 

Download / Print Reference Chart

 

 

 

It's not just about filling up the tank. The volume of oil occupies a significant portion of the transformer's total
weight and plays two critical roles: Electrical Insulation and Thermal Cooling.

 

Cooling Efficiency

The oil acts as a primary coolant in liquid-filled transformers. If the volume is too low (e.g., due to a leak or improper filling), the effective heat dissipation surface area in the radiators is significantly reduced.

 

This leads to:

• Hotspots in the copper or aluminum windings.
• Accelerated aging of the solid paper insulation (DP value drops).
• Potential thermal runaway and reduced lifespan.

 

 

Insulation Distance

In higher voltage transformers (like 11kV, 33kV, or 66kV), the oil provides the necessary dielectric clearance
between live parts and the grounded tank. A critically low oil level can expose live parts (like the tap changer
mechanism or high-voltage bushings) to air. Since air has a much lower dielectric strength than oil, this can lead to an immediate internal flashover.

 

 

If you have a vintage transformer with a missing or unreadable nameplate, how do you estimate the oil volume?

 

While precision is impossible without the manufacturer's drawings, you can use these rough estimation factors for
standard oil-immersed transformers:

 

• Small (up to 100 kVA): ~ 1.8 to 2.2 Liters per kVA (Round tank designs often hold more oil
• relative to core size)
• Medium (100 – 500 kVA): ~ 1.4 to 1.6 Liters per kVA
• Large (500 – 2500 kVA): ~ 1.0 to 1.3 Liters per kVA

 

Note: As transformers get larger, the core and coil become denser, and the ratio of oil to kVA typically decreases, although the absolute volume increases significantly due to large radiators.

 

Calculation Example

For a standard 500 kVA distribution transformer:

• 500 kVA × 1.5 L/kVA ≈ 750 Liters

This estimation aligns well with our chart range of 650-800 Liters.

 

 

Now that you know the capacity, maintaining that oil is key to the transformer's longevity. Regular testing ensures
your transformer runs efficiently.

Parameter	Recommended Limit (Service)	Testing Frequency
Dielectric Strength (BDV)	> 50 kV (for < 72.5kV class)	Annually
Moisture Content (Water)	< 20 ppm	Annually
Acidity (Neutralization)	< 0.15 mg KOH/g	Every 2 years
Interfacial Tension (IFT)	> 25 mN/m	Every 2 years
Flash Point	> 135°C	Every 3-5 years

 

To learn more about the oil itself, check out our Complete Guide to Transformer Oil.

 

Need a replacement transformer?

 

Whether you need a 30-2500KVA oil-filled-transformer or a 30-2500KVA dry type transformer, we can manufacture it to your exact specifications with the optimal oil capacity. Contact us today for a quote.

 

Request A Quote

 

 

What is the capacity of oil in a transformer?

Typically, the oil capacity in transformers can range from a few hundred liters for smaller units to several thousand liters for large power transformers. This oil serves as both an insulator and a coolant, ensuring efficient operation and preventing overheating during electrical load conditions.

 

How much oil is in a 200 kVA transformer?

For 200kVA three-phase Distribution Transformers, the oil in it is about 160KG.

 

How many liters of oil are in a 100 kVA transformer?

Typical Oil to kVA Ratios

Transformer Power Rating (kVA)	Oil Volume Range (Liters)
Up to 100 kVA	50 to 200 liters
100 kVA to 1,000 kVA	200 to 1,500 liters
1 MVA to 10 MVA	1,000 to 5,000 liters
10 MVA to 50 MVA	5,000 to 15,000 liters

 

What is the oil capacity of a 25 kw transformer?

The oil capacity of a 25 kVA transformer is typically around 40 to 60 liters

 

How much oil does a 33KV transformer hold?

The document lists oil quantities for different types and sizes of power transformers. A 132/33KV, 50MVA transformer uses an average of 21KL of oil. A 220/132/33KV, 160MVA auto transformer uses 51KL of oil.

 

How much oil does a 500 kVA transformer hold?

The oil capacity of a 500 kVA transformer is typically around 400 to 600 liters. The exact amount can vary depending on the design and specific manufacturer.

 

What is the 80% rule for transformers?

The 80% rule is a guideline that recommends operating a transformer at no more than 80% of its rated capacity under normal conditions. For example, if a power pole transformer is rated for 50 kVA, it should ideally carry no more than 40 kVA during continuous operation.