{
  "slug": "weight-balance-cg-margin",
  "title": "Weight and Balance CG Margin Calculator",
  "heading": "Weight and Balance CG Margin Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/weight-balance-cg-margin",
  "summary": "How much margin you have to forward and aft CG limits, not just pass/fail.",
  "description": "A basic weight and balance check tells you pass or fail. This one goes further and tells you how many inches of margin you have to each limit, which matters because a CG near the aft limit degrades stall recovery and stability margins even when it's technically within limits. It sums moments from empty weight, pilot/passengers, fuel, and baggage stations, divides by total weight to find CG, and reports the margin to both the forward and aft limits along with whether you're within the max gross weight.",
  "formula": "CG = total moment ÷ total weight, where moment = weight × arm for each station. Margin = CG − forward limit, and aft limit − CG.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=weight-balance-cg-margin",
  "inputs": [
    {
      "id": "emptyWeight",
      "label": "Empty weight",
      "kind": "number",
      "hint": null,
      "default": 1600,
      "unit": "lb",
      "min": 0,
      "max": null
    },
    {
      "id": "emptyArm",
      "label": "Empty weight arm",
      "kind": "number",
      "hint": null,
      "default": 39.5,
      "unit": "in",
      "min": 0,
      "max": null
    },
    {
      "id": "frontWeight",
      "label": "Front seats total weight",
      "kind": "number",
      "hint": null,
      "default": 340,
      "unit": "lb",
      "min": 0,
      "max": null
    },
    {
      "id": "frontArm",
      "label": "Front seats arm",
      "kind": "number",
      "hint": null,
      "default": 37,
      "unit": "in",
      "min": 0,
      "max": null
    },
    {
      "id": "fuelGal",
      "label": "Fuel weight",
      "kind": "number",
      "hint": null,
      "default": 40,
      "unit": "gal",
      "min": 0,
      "max": null
    },
    {
      "id": "fuelArm",
      "label": "Fuel arm",
      "kind": "number",
      "hint": null,
      "default": 48,
      "unit": "in",
      "min": 0,
      "max": null
    },
    {
      "id": "baggage",
      "label": "Baggage weight",
      "kind": "number",
      "hint": null,
      "default": 40,
      "unit": "lb",
      "min": 0,
      "max": null
    },
    {
      "id": "baggageArm",
      "label": "Baggage arm",
      "kind": "number",
      "hint": null,
      "default": 95,
      "unit": "in",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "cg",
      "label": "Computed CG",
      "format": "decimal",
      "hint": null,
      "primary": true
    },
    {
      "id": "totalWeight",
      "label": "Total weight",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "marginFwd",
      "label": "Margin to forward limit (in)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "marginAft",
      "label": "Margin to aft limit (in)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "overGross",
      "label": "Lb over max gross (negative = under)",
      "format": "number",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Empty weight: 1600 lb",
      "Empty weight arm: 39.5 in",
      "Front seats total weight: 340 lb",
      "Front seats arm: 37 in",
      "Fuel weight: 40 gal",
      "Fuel arm: 48 in",
      "Baggage weight: 40 lb",
      "Baggage arm: 95 in"
    ],
    "outputs": [
      "Computed CG: 41.04",
      "Total weight: 2,220",
      "Margin to forward limit (in): 6.04",
      "Margin to aft limit (in): 6.26",
      "Lb over max gross (negative = under): -230"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter empty weight (lb).",
      "Enter empty weight arm (in).",
      "Enter front seats total weight (lb).",
      "Enter front seats arm (in).",
      "Enter fuel weight (gal).",
      "Enter fuel arm (in).",
      "Enter baggage weight (lb).",
      "Enter baggage arm (in).",
      "Read your computed cg 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": {
        "emptyWeight": 960,
        "emptyArm": 23.7,
        "frontWeight": 205,
        "frontArm": 22.2,
        "fuelGal": 24,
        "fuelArm": 28.799999999999997,
        "baggage": 25,
        "baggageArm": 57
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "emptyWeight": 1600,
        "emptyArm": 39.5,
        "frontWeight": 340,
        "frontArm": 37,
        "fuelGal": 40,
        "fuelArm": 48,
        "baggage": 40,
        "baggageArm": 95
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "emptyWeight": 2560,
        "emptyArm": 63.2,
        "frontWeight": 545,
        "frontArm": 59.2,
        "fuelGal": 64,
        "fuelArm": 76.80000000000001,
        "baggage": 65,
        "baggageArm": 152
      }
    }
  ],
  "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": "Why use a generic forward/aft limit instead of my POH numbers?",
      "a": "The default limits shown (35.0 to 47.3 inches) are illustrative placeholder values modeled on a common trainer. Every make and model has its own envelope, and some airplanes have limits that shift with total weight rather than being fixed numbers, so you must substitute your specific POH's forward and aft CG limits for a real preflight check."
    },
    {
      "q": "Why does aft CG matter even if I'm within limits?",
      "a": "As CG moves aft, static longitudinal stability decreases and stall recovery becomes more difficult because there's less elevator authority to counter a nose-up pitching moment. An airplane loaded near the aft limit can still be legal but noticeably less forgiving in slow flight and stalls than one loaded mid-envelope."
    },
    {
      "q": "How is fuel weight calculated here?",
      "a": "This tool assumes 6 lb/gal for standard 100LL avgas. Jet A weighs about 6.7-6.8 lb/gal depending on temperature, so turbine aircraft or diesel-cycle piston engines need that substituted before trusting the total weight figure."
    },
    {
      "q": "What if I'm over gross but within CG limits?",
      "a": "Being within the CG envelope doesn't override a max gross weight violation — both must be satisfied independently. Exceeding max gross weight, even by a small margin, is a certification violation with real structural and performance consequences: longer takeoff roll, reduced climb rate, and higher stall speed."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/density-altitude-takeoff-penalty",
    "https://www.revenuelab.fyi/toolbox/fuel-endurance-range",
    "https://www.revenuelab.fyi/toolbox/climb-performance-fuel"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Weight and Balance CG Margin Calculator (https://www.revenuelab.fyi/toolbox/weight-balance-cg-margin)"
}