Generator Sizing (DC) Calculator

Diesel engines rely on air density for combustion, and thinner air at altitude reduces the engine's achievable output. This calculator applies a 3.5% derate for every 1,000 feet above the first 1,000 feet of altitude, which directly reduces the generator's effective capacity — so a generator that would be adequate at sea level may need to be substantially larger at a high-elevation site to deliver the same real-world kW.

Altitude derate (3.5% per 1,000ft above 1,000ft) and temperature derate (1% per 5°F above 104°F) are added together into a single combined percentage, which is then capped at 40% total regardless of how extreme the inputs get. That combined derate divides into the facility's kVA requirement to determine the actual generator capacity needed, so a hot, high-altitude site can require notably more nameplate capacity than the raw facility load alone would suggest.

Generators can't instantly accept their full rated load in one step — doing so risks stalling the engine — so the max step load percentage input caps how much load can be applied at once, computed as generator size × power factor × that percentage. Load transfer steps is the full facility load divided by that per-step capacity, rounded up, telling you how many sequential breaker closures or load banks are needed to bring the whole IT load online safely.

The fuel figure uses a rule-of-thumb consumption rate of about 7 gallons per hour per 100kW at 75% load, multiplied out to 48 hours — a common Tier III fuel-autonomy benchmark, but a generic one. Actual fuel burn varies by specific generator model, real load profile, and ambient conditions, so treat this as a planning-stage estimate and confirm exact consumption against your chosen generator's fuel curve before sizing a fuel tank or delivery contract.