{
  "slug": "generator-sizing-fuel",
  "title": "Generator Sizing & Fuel Cost Calculator",
  "heading": "Generator Sizing & Fuel Cost Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/generator-sizing-fuel",
  "summary": "Right-size a generator and estimate fuel cost per outage.",
  "description": "Sizes a portable or standby generator from your selected running and starting loads, then estimates fuel burn and cost for a given outage length. Generators are rated by running watts and a higher surge watts figure; if your total starting load (the largest single motor's startup surge plus everything else already running) exceeds the surge rating, the generator will stall or trip. This tool checks that headroom and converts wattage into gallons of gas, propane, or diesel per hour using typical fuel-consumption curves so you can budget for a multi-day outage instead of guessing at the pump.",
  "formula": "Fuel gal/hr ≈ (load% × rated fuel curve); total fuel = fuel/hr × outage hours; cost = total fuel × price/gal.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=generator-sizing-fuel",
  "inputs": [
    {
      "id": "runningWatts",
      "label": "Total running load",
      "kind": "number",
      "hint": null,
      "default": 5000,
      "unit": "W",
      "min": 200,
      "max": null
    },
    {
      "id": "surgeWatts",
      "label": "Largest single startup surge",
      "kind": "number",
      "hint": null,
      "default": 3000,
      "unit": "W",
      "min": 0,
      "max": null
    },
    {
      "id": "genRunningRating",
      "label": "Generator running watt rating",
      "kind": "number",
      "hint": null,
      "default": 7500,
      "unit": "W",
      "min": 500,
      "max": null
    },
    {
      "id": "genSurgeRating",
      "label": "Generator surge watt rating",
      "kind": "number",
      "hint": null,
      "default": 9500,
      "unit": "W",
      "min": 500,
      "max": null
    },
    {
      "id": "fuelType",
      "label": "Fuel type",
      "kind": "select",
      "hint": null,
      "default": "gas",
      "options": [
        {
          "value": "gas",
          "label": "Gasoline (~0.6 gal/hr per 5kW load at 50%)"
        },
        {
          "value": "propane",
          "label": "Propane (~1.2 gal/hr equivalent)"
        },
        {
          "value": "diesel",
          "label": "Diesel (~0.45 gal/hr per 5kW load)"
        }
      ]
    },
    {
      "id": "fuelPrice",
      "label": "Fuel price",
      "kind": "number",
      "hint": null,
      "default": 3.5,
      "unit": "$/gal",
      "min": 0.5,
      "max": null
    },
    {
      "id": "outageHours",
      "label": "Expected outage length",
      "kind": "number",
      "hint": null,
      "default": 48,
      "unit": "hrs",
      "min": 1,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "totalCost",
      "label": "Total fuel cost for outage",
      "format": "currency",
      "hint": null,
      "primary": true
    },
    {
      "id": "galPerHr",
      "label": "Fuel burn rate",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "totalFuel",
      "label": "Total fuel needed",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "runningOk",
      "label": "Running load fits? (1=yes)",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "surgeOk",
      "label": "Surge load fits? (1=yes)",
      "format": "number",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Total running load: 5000 W",
      "Largest single startup surge: 3000 W",
      "Generator running watt rating: 7500 W",
      "Generator surge watt rating: 9500 W",
      "Fuel type: Gasoline (~0.6 gal/hr per 5kW load at 50%)",
      "Fuel price: 3.5 $/gal",
      "Expected outage length: 48 hrs"
    ],
    "outputs": [
      "Total fuel cost for outage: $121",
      "Fuel burn rate: 0.72",
      "Total fuel needed: 34.6",
      "Running load fits? (1=yes): 1",
      "Surge load fits? (1=yes): 1"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter total running load (W).",
      "Enter largest single startup surge (W).",
      "Enter generator running watt rating (W).",
      "Enter generator surge watt rating (W).",
      "Enter fuel type.",
      "Enter fuel price ($/gal).",
      "Enter expected outage length (hrs).",
      "Read your total fuel cost for outage on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "runningWatts": 3000,
        "surgeWatts": 1800,
        "genRunningRating": 4500,
        "genSurgeRating": 5500,
        "fuelType": "gas",
        "fuelPrice": 2.1,
        "outageHours": 29
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "runningWatts": 5000,
        "surgeWatts": 3000,
        "genRunningRating": 7500,
        "genSurgeRating": 9500,
        "fuelType": "gas",
        "fuelPrice": 3.5,
        "outageHours": 48
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "runningWatts": 8000,
        "surgeWatts": 4800,
        "genRunningRating": 12000,
        "genSurgeRating": 15000,
        "fuelType": "gas",
        "fuelPrice": 5.6000000000000005,
        "outageHours": 77
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "How do I size running watts for my house?",
      "a": "Add up the running wattage of everything you'd run simultaneously: fridge (150W), sump pump (800-1300W), furnace blower (600-1000W), a few circuits of lights and outlets (600W), and a window AC if needed (1000-1500W). A 5,000-7,500W generator covers most partial-home setups; a whole-house standby unit typically runs 16,000-22,000W."
    },
    {
      "q": "Why is surge rating separate from running rating?",
      "a": "Motors draw 2-3x rated running watts for under a second at startup. A generator with 7,500 running watts might only handle 9,000-9,500 surge watts, so if your well pump surges to 3,000W while your furnace and fridge are already running, you can trip the generator's breaker even though average load looks fine."
    },
    {
      "q": "Propane vs gasoline for backup power?",
      "a": "Propane stores indefinitely without degrading (gasoline goes stale in 3-6 months without stabilizer), burns cleaner, and is safer to store in bulk, but delivers about 10-15% less energy per gallon so burn rate is higher. Gas is cheaper per gallon and more available during regional outages; propane is better for planned, infrequent backup."
    },
    {
      "q": "How much fuel should I stock for a multi-day outage?",
      "a": "For a mid-size 7,500W generator at moderate load, expect 15-20 gallons of gas per day. A 5-day outage needs 75-100 gallons — well beyond safe residential gasoline storage limits in most areas, which is a strong argument for a natural gas or larger propane standby unit if you live somewhere with frequent multi-day outages."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/battery-backup-runtime",
    "https://www.revenuelab.fyi/toolbox/generator-transfer-switch",
    "https://www.revenuelab.fyi/toolbox/whole-home-load-calc"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Generator Sizing & Fuel Cost Calculator (https://www.revenuelab.fyi/toolbox/generator-sizing-fuel)"
}