How Much Diesel Does a Data Center Need? Sizing Fuel by MW and Runtime

How much diesel a data center needs: the formula

Then divide by the share of each tank you can actually pump out to get tank capacity. Each input is a decision, not a constant:

1. IT load (kW). The critical load in the halls at the build-out you're designing for. A campus that fills over years needs the math re-run at each phase.
2. Overhead factor. Generators carry the whole building: cooling, UPS and distribution losses, lighting. PUE, the metric The Green Grid introduced in 2007, is total facility power divided by IT power. Uptime Institute's 2025 survey put the weighted average annual PUE at 1.54, and 1.44 for data centers of 20 MW and up. That's an annual average. Fuel has to cover the peak, so use your engineer's peak demand figure where you have one.
3. Gallons per kWh. Across 28 manufacturer spec sheets in our generator fuel consumption chart, the median is 0.074 gallons per kWh at full load and 0.079 at 75%. It rises at light load: 0.083 at 50%, 0.089 at 25%.
4. Runtime (hours). Set by your design standard, your customers and your code, covered below.

Diesel per megawatt: 24, 48 and 72 hours

At 0.079 gallons per kWh (the 75% load median), every megawatt the generators carry burns 79 gallons an hour. Usable fuel by generator load and runtime:

Usable U.S. gallons. Generator load is the total kW on the generators, not IT load. At full load (0.074 gal/kWh) every figure drops about 6%. The highlighted row is the worked example below.

Starting from IT load? Multiply by your overhead factor first. At 1.5, each IT megawatt is 1.5 MW on the generators: about 119 gallons an hour, or roughly 2,840 gallons a day.

Why the rule holds. EIA puts a gallon of diesel at 137,381 Btu and a kWh at 3,412 Btu, so a gallon holds about 40 kWh of heat. At 0.074 gallons per kWh, a generator turns about a third of that into electricity. Models differ (at full load the sheets in our chart run from about 0.060 to 0.093 gallons per kWh), which is why your own sheets win. But the rate is per kWh, so it scales from one set to a whole plant.

Worked example: fuel for a hypothetical 10 MW data center

A made-up facility, to show the method. Assumptions: 10,000 kW of IT load at full build-out; peak overhead factor 1.5, close to the industry average PUE; 2,000 kW generators with a rating that has no runtime limit; N+1 redundancy; one fuel tank per generator; a 72-hour target; 80–85% of each tank usable.

1. Generator load. 10,000 kW IT × 1.5 = 15,000 kW on the generators.
2. Generator count. 15,000 ÷ 2,000 = 7.5, so N = 8 sets. N+1 = 9 sets. Sharing the load, each carries about 1,667 kW, or 83% of its rating. That's the same arithmetic as a published engineering example, where a 10 MW load on 2 MW sets takes five for N and six for N+1 (Consulting-Specifying Engineer).
3. Burn rate. 15,000 kW × 0.079 gal/kWh = 1,185 gallons an hour. At 83% per set, the true median sits between 0.079 and 0.074, so this leans conservative. Cross-check: Cat's 3516C sheet at its 2,250 ekW data center rating (Prime-DCP) lists 119.7 gph at 75% load and 151.7 at 100%, or 0.071 and 0.067 gallons per kWh. At those rates the plant burns about 1,010–1,065 gph. Plan on the higher number unless you have your own sets' sheets.
4. Usable fuel. 1,185 gph × 72 h = 85,320 usable gallons.
5. Tank capacity. Consulting-Specifying Engineer puts usable fuel at typically 80–85% of tank capacity. 85,320 ÷ 0.85 = 100,376 and 85,320 ÷ 0.80 = 106,650, so about 100,000–107,000 gallons of nominal capacity.
6. Redundancy. Uptime Institute evaluates fuel storage with the redundant components removed. If the ninth generator's tank goes out of service with it, the other eight tanks must hold the 72 hours: 85,320 ÷ 8 = 10,665 usable gallons each, or about 12,550–13,330 gallons of capacity per tank.

Example facility: 15,000 kW generator load at 1,185 gph. Transport loads = usable gallons ÷ 7,500, rounded up, filling from empty.

How many hours of fuel: 12, 24, 48, 72 or more

No single number applies to every data center. Several sources set it, and the strictest one wins:

• Uptime Institute Tier Standard. A minimum of 12 hours of on-site fuel for all Tiers, at N load, while still meeting the site's topology objective (concurrently maintainable or fault tolerant). Uptime calls 12 hours a starting point.
• Hyperscale practice. Microsoft's public datacenter fact sheet says its sites store enough fuel to run the generators for up to 48 hours, with one tank per generator.
• Engineering practice. Consulting-Specifying Engineer notes that critical facilities such as data centers are typically expected to support the load for 24 hours or more, depending on resiliency requirements.
• NFPA 110, where it applies. The Class is the minimum time, in hours, the system is designed to run at its rated load without refueling: 0.083, 0.25, 2, 6 or 48 hours, or Class X for a time set by the application, code or user.
• Your customers. If a colocation contract or SLA promises a runtime, that number goes into the formula.

Two cautions. Hours on paper aren't hours in the tank: Uptime's example is a site claiming 48 hours that has two 24-hour tanks, which is 24 hours once one tank is out for maintenance. And on-site fuel only has to bridge until the trucks arrive. The longer the target, the more the resupply plan matters (see below). Code requirements, fuel SLAs and air-permit runtime limits each deserve their own discussion; this guide stays on the math.

Design load vs. the load you'll actually see

Size fuel on design load. Uptime's 12 hours are at N load, and NFPA 110 Classes are defined at rated load. That's the right basis, because the hall will fill.

Expect a lighter real load. Cummins describes a load of about 36–39% of the generator system's rating as "very common in real-world data centers." At light load each set burns fewer gallons an hour but more per kWh. In the example, if the plant carried 6,000 kW (40% of design), each of the nine sets would run at about a third of its rating, at roughly 0.083–0.089 gallons per kWh: about 500–535 gph. The same 85,320 gallons would last about 160–170 hours. Treat that as margin, not a reason to buy a smaller tank.

Read the right column on the spec sheet. In Tier III and IV, Uptime treats the generators as the primary power source, so they must carry the entire load with no limit on run hours (Cummins). Standard ISO standby ratings cap run time, so manufacturers publish data center ratings with no hourly limit: Cummins DCC, Cat Prime-DCP. Each rating has its own kW figure and fuel table. Take the fuel figures from the rating you actually bought. The chart's spec sheet guide covers the rest.

What else draws on the tank

From gallons to trucks: what your runtime means for deliveries

On-site storage buys time. Deliveries keep the plant running after it's used up. In the example, the plant burns 1,185 gallons an hour:

• 28,440 gallons a day just to hold steady, about 3.8 transport loads of 7,500 gallons.
• One full transport every 6 hours and 20 minutes (7,500 ÷ 1,185 = 6.3 hours), around the clock.
• 12 transport loads to refill 72 hours of usable fuel from empty.

That's why the delivery plan has to exist before the outage: which tanks get filled in what order, how many trucks that takes, and how they get through security and onto the fill points. More on running a data center fuel program on our data center fuel delivery page, and the bigger picture in our data center backup generator guide.

Generator plant fuel, planned back from your runtime

FuelGo works back from the runtime you've committed to: the volume that has to be on site and the refill rate that sustains it once the generators carry the building. We deliver dyed diesel for stationary generators, clear diesel and R99 renewable diesel nationwide, 20 to 4,400 gallons per drop and transport loads up to 7,500 gallons through our bulk fuel delivery. Generator fuel programs combine a keep-full schedule set from your test schedule and consumption history, monitored tanks that trigger refills on actual consumption, and an outage response plan agreed in advance: delivery sequence, truck count and site access.

During regional outages, critical facilities like data centers are prioritized in emergency dispatch, and dispatch is staffed 24/7/365. Need more runtime than the sub-base tanks hold? Rental day and auxiliary tanks extend it. Stored fuel gets lab fuel testing and polishing for tanks from 50 to 50,000 gallons. Every fill is itemized by gallons, date and tank, with invoicing through ARIBA or COUPA if you use them. Get a free quote or call 800-720-4546; a dispatcher replies within the hour.

Data center diesel sizing FAQ

Sources: Uptime Institute Journal, Fuel System Design and Reliability (12 hours at N for all Tiers; redundant components removed; 48-hour/two-tank example) · Uptime Institute Global Data Center Survey 2025 (PUE definition, 1.54 weighted average, 1.44 at 20 MW and up) · Cummins, Data Center Continuous (DCC) Ratings white paper (Tier III/IV primary power, no run-hour limit, ISO ratings, 36–39% load) · Caterpillar 3516C Prime-DCP 2,250 ekW spec sheet, LEHE2680-02 (dealer copy) · Kohler KD2000 spec sheet G5-626 (HVO/RD up to 4% more by volume) · Consulting-Specifying Engineer, The nine major steps of designing generator fuel systems (24 hours or more; 80–85% usable) · Consulting-Specifying Engineer, NFPA 110-2019 concepts and changes (Class definition) · Consulting-Specifying Engineer, Paralleled Generator System Considerations (10 MW on 2 MW sets, N+1) · Microsoft, Datacenter fuel safety and sustainability fact sheet (up to 48 hours, one tank per generator) · U.S. EIA, British thermal units (diesel 137,381 Btu/gal; 3,412 Btu/kWh). Gallons-per-kWh medians are from the 28 spec sheets in our generator fuel consumption chart. The worked example, per-MW table, truck counts and efficiency figure are FuelGo calculations from these sources.