{
  "slug": "generator-sizing",
  "title": "Generator Sizing Calculator",
  "heading": "Home Generator Sizing Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/generator-sizing",
  "summary": "Running and starting watts needed for your backup loads.",
  "description": "Motors draw two to three times their running wattage on startup. Sizing to running watts alone is the classic mistake that trips a generator the moment the well pump kicks on.",
  "formula": "Required = Sum of running watts + largest starting surge.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=generator-sizing",
  "inputs": [
    {
      "id": "fridge",
      "label": "Refrigerators",
      "kind": "number",
      "hint": null,
      "default": 1,
      "unit": null,
      "min": 0,
      "max": 5
    },
    {
      "id": "sumpPump",
      "label": "Sump or well pumps",
      "kind": "number",
      "hint": null,
      "default": 1,
      "unit": null,
      "min": 0,
      "max": 4
    },
    {
      "id": "furnace",
      "label": "Furnace blowers",
      "kind": "number",
      "hint": null,
      "default": 1,
      "unit": null,
      "min": 0,
      "max": 3
    },
    {
      "id": "lights",
      "label": "Lighting load",
      "kind": "number",
      "hint": null,
      "default": 400,
      "unit": "W",
      "min": 0,
      "max": null
    },
    {
      "id": "electronics",
      "label": "Electronics and networking",
      "kind": "number",
      "hint": null,
      "default": 300,
      "unit": "W",
      "min": 0,
      "max": null
    },
    {
      "id": "ac",
      "label": "Window AC units",
      "kind": "number",
      "hint": null,
      "default": 0,
      "unit": null,
      "min": 0,
      "max": 4
    },
    {
      "id": "microwave",
      "label": "Microwaves",
      "kind": "number",
      "hint": null,
      "default": 1,
      "unit": null,
      "min": 0,
      "max": 3
    },
    {
      "id": "fuelRate",
      "label": "Fuel cost",
      "kind": "number",
      "hint": null,
      "default": 3.6,
      "unit": "$/gal",
      "min": 0.5,
      "max": 12
    }
  ],
  "outputs": [
    {
      "id": "recommended",
      "label": "Recommended generator size (W)",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "running",
      "label": "Total running watts",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "surge",
      "label": "Peak starting watts",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "gph",
      "label": "Estimated fuel burn (gal/hr)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "dailyFuel",
      "label": "Fuel cost for 12 hours",
      "format": "currency",
      "hint": null,
      "primary": false
    },
    {
      "id": "required",
      "label": "Calculated requirement (W)",
      "format": "number",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Refrigerators: 1",
      "Sump or well pumps: 1",
      "Furnace blowers: 1",
      "Lighting load: 400 W",
      "Electronics and networking: 300 W",
      "Window AC units: 0",
      "Microwaves: 1",
      "Fuel cost: 3.6 $/gal"
    ],
    "outputs": [
      "Recommended generator size (W): 6,500",
      "Total running watts: 4,100",
      "Peak starting watts: 6,100",
      "Estimated fuel burn (gal/hr): 0.55",
      "Fuel cost for 12 hours: $23.72",
      "Calculated requirement (W): 6,100"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter refrigerators.",
      "Enter sump or well pumps.",
      "Enter furnace blowers.",
      "Enter lighting load (W).",
      "Enter electronics and networking (W).",
      "Enter window ac units.",
      "Enter microwaves.",
      "Enter fuel cost ($/gal).",
      "Read your recommended generator size (w) 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": {
        "fridge": 1,
        "sumpPump": 1,
        "furnace": 1,
        "lights": 250,
        "electronics": 200,
        "ac": 0,
        "microwave": 1,
        "fuelRate": 2.16
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "fridge": 1,
        "sumpPump": 1,
        "furnace": 1,
        "lights": 400,
        "electronics": 300,
        "ac": 0,
        "microwave": 1,
        "fuelRate": 3.6
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "fridge": 2,
        "sumpPump": 2,
        "furnace": 2,
        "lights": 650,
        "electronics": 500,
        "ac": 0,
        "microwave": 2,
        "fuelRate": 5.760000000000001
      }
    }
  ],
  "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 does the home generator sizing calculator work?",
      "a": "Motors draw two to three times their running wattage on startup. Sizing to running watts alone is the classic mistake that trips a generator the moment the well pump kicks on. The underlying maths is: Required = Sum of running watts + largest starting surge."
    },
    {
      "q": "What do I need to enter?",
      "a": "8 values: refrigerators, sump or well pumps, furnace blowers, lighting load, electronics and networking, window ac units, microwaves, and fuel cost. Each field starts with a sensible default, so you can change one number at a time and watch the result move."
    },
    {
      "q": "What does the recommended generator size (w) result mean?",
      "a": "It is returned as a whole number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds."
    },
    {
      "q": "Is this calculator free, and do I need an account?",
      "a": "Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser."
    },
    {
      "q": "How accurate is the result?",
      "a": "It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary."
    },
    {
      "q": "Who is this tool for?",
      "a": "It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/electricity-cost",
    "https://www.revenuelab.fyi/toolbox/hvac-run-cost"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Generator Sizing Calculator (https://www.revenuelab.fyi/toolbox/generator-sizing)"
}