Generator Fuel Consumption Chart: Diesel Gallons per Hour by kW and Load
Gallons per hour at 25, 50, 75 and 100% load for 20 kW to 2,000 kW diesel sets, taken from Cummins, Caterpillar, Generac and Kohler spec sheets.
A diesel generator burns about 0.074 gallons per hour per kW at full load, the median of 28 manufacturer spec sheets. At 75% load it's about 0.059 gph per kW, at 50% about 0.042 and at 25% about 0.022. A 500 kW set at 75% load burns roughly 25 gallons an hour. Your spec sheet has the exact figure.
Want your own number? Enter kW, load, run hours and your diesel price in the generator fuel calculator for gallons per hour, per day and per week, plus the fuel cost.
Open the calculator →Diesel generator fuel consumption chart (gallons per hour)
Every figure below comes from a manufacturer's published spec sheet: 60 Hz sets on #2 diesel, at the standby rating. Where two makers publish a set of the same size, the chart shows both as a range. Values are rounded to one decimal.
| Standby kW | 25% | 50% | 75% | 100% |
|---|---|---|---|---|
| 20 kWGenerac SD020 | 0.8 | 1.1 | 1.4 | 1.7 |
| 30 kWGenerac SD030 | 1.0 | 1.4 | 2.0 | 2.8 |
| 40 kWGenerac SD040, Cummins C40D6R | 1.1 | 1.9 | 2.4– | 3.4– |
| 50 kWGenerac SD050 | 1.3 | 2.3 | 3.3 | 4.3 |
| 60 kWGenerac SD060, Cummins C60D6R | 1.4– | 2.7 | 3.6– | 4.8– |
| 80 kWGenerac SD080 | 2.1 | 3.7 | 5.2 | 6.3 |
| 100 kWGenerac SD100, Cat D100 GC | 2.2* | 4.2– | 5.9 | 7.3– |
| 130 kWGenerac SD130 | 2.9 | 5.4 | 7.7 | 9.6 |
| 150 kWGenerac SD150 | 3.3 | 6.2 | 8.8 | 11.2 |
| 175 kWGenerac SD175 | 3.9 | 7.3 | 10.5 | 13.5 |
| 200 kWGenerac SD200, Kohler 200REOZJF | 4.4– | 8.3 | 11.4– | 14.8– |
| 250 kWGenerac SD250 | 5.5 | 10.4 | 14.8 | 18.5 |
| 300 kWGenerac SD300 | 7.6 | 12.6 | 17.4 | 22.1 |
| 350 kWCummins C350 D6 | 6.6 | 11.1 | 15.8 | 21.1 |
| 500 kWCat C15 | 10.7 | 17.9 | 25.1 | 32.5 |
| 550 kWKohler 550REOZVB | 10.4 | 19.1 | 28.8 | 39.9 |
| 700 kWKohler KD700 | 13.4 | 25.9 | 38.2 | 48.1 |
| 800 kWKohler KD800 | 17.3 | 31.2 | 44.6 | 57.5 |
| 1,000 kWGenerac SD1000, Kohler KD1000 | 22.2– | 38.6– | 55.3– | 70.9– |
| 1,500 kWGenerac SD1500, Kohler KD1500 | 32.8– | 58.6– | 83.5– | 105.9– |
| 2,000 kWCat 3516C, Kohler KD2000 | 43.4– | 75.1– | 104.1– | 133.6– |
U.S. gallons per hour at the percent of standby rating shown. *Cat's D100 GC sheet lists 50, 75 and 100% only, so the 25% figure is Generac's. The Cat C15 sheet is a non-certified (export) emissions rating; EPA-certified versions may differ. Spec sheet links are in the sources at the end. Figures are approximate: always check the sheet for your exact model.
Size not listed? The generator fuel calculator scales any kW rating and adds daily, weekly and yearly fuel cost.
Calculate fuel use →Diesel generator gallons per hour: the rule of thumb by load
Divide each sheet's gallons per hour by its kW rating and the sets line up closely. These are the medians across all 28 sheets, with the full spread:
| Load | Gal/hr per kW (median) | Spread across sheets | Gal per kWh made |
|---|---|---|---|
| 25% | 0.022 | 0.019–0.040 | 0.089 |
| 50% | 0.042 | 0.032–0.053 | 0.083 |
| 75% | 0.059 | 0.045–0.069 | 0.079 |
| 100% | 0.074 | 0.060–0.093 | 0.074 |
Our calculation from the spec sheets in the chart. "Gal per kWh" is gallons per hour divided by the kW actually produced at that load.
Example: a 400 kW set at 75% load burns about 400 × 0.059 = 24 gallons an hour. The full-load figure, 0.074 gph per kW, is the same rule of thumb our generator fuel delivery page uses.
How the calculator compares. The generator fuel calculator uses the same median rates per kW at 25%, 50%, 75% and 100% load as this chart. That's close enough for a budget. For a runtime you'll commit to in writing, use your own set's sheet.
Load mattersWhy a lightly loaded generator wastes fuel
Fuel burn doesn't fall in step with load. On the sheets in this chart, a set at 25% load still burns 26% to 48% of its full-load fuel, most of them close to 30%. So each kWh costs more at light load: about 0.089 gallons per kWh at 25% against 0.074 at full load, the medians in the table above.
That's why an oversized generator is expensive to run. It's also bad for the engine. NFPA 110 requires sets in emergency service to be exercised monthly for at least 30 minutes at no less than 30% of the standby nameplate kW, or at a load that keeps the maker's minimum exhaust temperature, because light loading causes wet stacking: unburned fuel and carbon in the exhaust. What that does to the engine, and how load banks fix it, is in our diesel generator maintenance guide.
Spec sheetsHow to read the fuel figures on your generator's spec sheet
- Find the right rating column. Most sheets list standby and prime separately. The prime rating is lower, so its gallons per hour are lower too. Cat defines standby as power for the length of a utility outage, averaging 70% of the standby rating, typically 200 hours a year and at most 500. Use the column that matches how you run the set.
- Load means percent of that rating. 75% of a 1,000 kW standby set is 750 kW. Read the actual kW off the controller during a test or an outage and use the load row closest to it.
- Burn rate isn't pump flow. Generac's sheets list fuel consumption and, separately, "total fuel pump flow (combustion + return)". On the SD100 that's 7.3 gph burned against 29.1 gph moved, with the rest returned to the tank. Size supply and return lines and day tanks to the pump flow, and plan fuel deliveries on the burn rate. Generac also notes the fuel supply installation must handle the 100% load rate.
- Test conditions. Cat reports fuel rates per ISO 3046-1, based on #2 diesel of 35° API gravity, and its figures include the radiator fan ("with fan"). Altitude and heat derate the set; the sheets cover that separately.
- Renewable diesel burns a little more by volume. Kohler's sheets note volumetric fuel consumption is up to 4% higher on HVO/renewable diesel than on #2 ULSD. If you switch to R99 renewable diesel, add that margin to your runtime math.
- Converting units. Liters per hour ÷ 3.785 = U.S. gallons per hour. For pounds per hour, multiply gallons by about 7.1 lb, the weight of a gallon of #2 diesel (see how much diesel weighs). A 1,000 kW set at full load burns roughly 500–590 lb of fuel an hour.
At 1,000 kW full load, Generac's SD1000 sheet lists 82.9 gph and Kohler's KD1000 lists 70.9. At 1,500 kW the gap is 133.0 against 105.9 gph. At 2,000 kW Cat and Kohler are closer: 133.6 and 139.6. Engines, emissions certification and ratings differ, so a chart can only give you the neighborhood. That's why the chart shows ranges, and why the sheet for your own model wins.
How long will your generator run? Outage and tank math
Use usable fuel, not tank capacity: the pickup sits above the tank floor. A 500 kW set at 75% load (25.1 gph on the Cat C15 sheet) runs about 40 hours on 1,000 usable gallons. The tank size calculator works it the other way, from runtime to tank size. Fuel needed at 75% load, from the chart:
| Generator | Gal/hr at 75% | 24-hour outage | 72-hour outage |
|---|---|---|---|
| 100 kW | 5.9 | ≈ 140 gal | ≈ 425 gal |
| 500 kW | 25.1 | ≈ 600 gal | ≈ 1,810 gal |
| 1,000 kW | 55.3–66.0 | ≈ 1,330–1,580 gal | ≈ 3,980–4,750 gal |
| 2,000 kW | 104.1–120.4 | ≈ 2,500–2,890 gal | ≈ 7,500–8,670 gal |
Gallons per hour × hours, rounded. A real outage swings between loads; plan on the highest load you expect.
NFPA 110 sizing. Where NFPA 110 applies, the system's Class is the minimum time, in hours, it must run at rated load without refueling: Class 0.083, 0.25, 2, 6, 48, or X for a duration set by code or the owner. California's HCAI checklist, which applies the 2025 edition, sizes the main tank at 133% of the low-fuel sensor quantity for classes of 24 hours or less, and 100% above 24 hours. It also requires tanks sized so the fuel is used within its storage life, or a plan to remediate or replace stale fuel. That's the case for a keep-full program over a giant tank; see how long diesel lasts. Your AHJ decides which edition applies.
TestingFuel for monthly exercise and annual load bank tests
Tests draw the tank down too, and they're easy to forget. Using the Cat C15 500 kW sheet:
- Monthly exercise (NFPA 110: at least 30 minutes at 30% or more of nameplate): about 12 gph at 30% load, interpolated between the 25% and 50% figures, so roughly 6 gallons per run.
- Annual supplemental load bank test, needed when monthly runs can't reach 30% (NFPA 110-2010: 50% of nameplate for 30 minutes, then 75% for 60 minutes, per the Minnesota Department of Health): 0.5 × 17.9 + 1 × 25.1 ≈ 34 gallons.
Editions and test rules differ; the details are in our maintenance guide and the generator maintenance checklist. Whatever the test burns, top the tank back up afterwards.
FuelGoGenerator fuel delivered on your burn rate
FuelGo delivers dyed off-road diesel to standby and prime generators nationwide, plus clear diesel and R99 renewable diesel. That's 20 to 4,400 gallons per drop, and transport loads up to 7,500 gallons, so a 72-hour reserve for a 1 MW set fits in one or two drops. Most sites mix three generator fuel programs: a keep-full schedule set from your test schedule and consumption history, monitored tanks that trigger refills on actual consumption, and emergency response with your site access already on file.
If the sub-base tank only buys hours, rental day tanks and auxiliary tanks stretch it to days. Stored fuel gets lab fuel testing, polishing and tank cleaning. Rooftop and high-rise sets: see rooftop generator fueling. Running a generator farm? See data center fuel delivery. Dispatch runs 24/7/365. Get a free quote or call 800-720-4546; a dispatcher replies within the hour.
Common questionsGenerator fuel consumption FAQ
How much diesel does a generator use per hour?
How many gallons per hour does a 100 kW diesel generator use?
How much fuel does a 500 kW generator use per hour?
How much fuel does a 1 MW generator use per hour?
Does a generator use less fuel at lower load?
How long will a generator run on a full tank?
Why is my generator using more fuel than the chart says?
Is the generator fuel calculator accurate?
Sources: Generac spec sheets: SD020 · SD030 · SD040 · SD050 · SD060 · SD080 · SD100 · SD130 · SD150 · SD175 · SD200 · SD250 · SD300 · SD1000 · SD1500. Cummins data sheets: C40D6R (D-6565) · C60D6R (D-6567) · C350 D6 (distributor copy). Caterpillar spec sheets (dealer copies): D100 GC · C15 500 ekW (LEHE1640) · 3516C 2000 ekW. Kohler spec sheets: 200REOZJF (G5-373) · 550REOZVB (G5-395) · KD700 (G5-624) · KD800 (G5-578) · KD1000 (G5-580) · KD1500 (G5-582) · KD2000 (G5-626). Codes: NFPA 110 first revisions, 8.4.2 monthly exercise · Minnesota Department of Health, generator testing requirements (NFPA 110-2010 8.4.2.3) · California HCAI, 2025 aboveground fuel storage EPSS checklist (NFPA 110-2025) · Consulting-Specifying Engineer, NFPA 110 classes. Medians, ranges, runtimes and test-fuel figures are FuelGo calculations from these sheets.