{
  "slug": "voltage-drop",
  "title": "Voltage Drop Calculator",
  "heading": "Wire Voltage Drop Calculator",
  "category": "math",
  "url": "https://www.revenuelab.fyi/toolbox/voltage-drop",
  "summary": "Check drop across a run before you pull the wire.",
  "description": "Long runs bleed voltage. Codes generally want branch-circuit drop under 3%. This estimates drop from length, current, and copper wire area.",
  "formula": "Vdrop = 2 × K × I × L ÷ CM (K ≈ 12.9 for copper)",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=voltage-drop",
  "inputs": [
    {
      "id": "volts",
      "label": "System voltage",
      "kind": "number",
      "hint": null,
      "default": 120,
      "unit": "V",
      "min": 1,
      "max": null
    },
    {
      "id": "amps",
      "label": "Load current",
      "kind": "number",
      "hint": null,
      "default": 15,
      "unit": "A",
      "min": 0.1,
      "max": null
    },
    {
      "id": "length",
      "label": "One-way run length",
      "kind": "number",
      "hint": null,
      "default": 100,
      "unit": "ft",
      "min": 1,
      "max": null
    },
    {
      "id": "cm",
      "label": "Wire area (circular mils)",
      "kind": "number",
      "hint": "12 AWG ≈ 6530, 10 AWG ≈ 10380",
      "default": 6530,
      "unit": null,
      "min": 100,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "pct",
      "label": "Voltage drop (%)",
      "format": "decimal",
      "hint": null,
      "primary": true
    },
    {
      "id": "drop",
      "label": "Drop (V)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "endVolts",
      "label": "Voltage at load",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "ok",
      "label": "Verdict",
      "format": "raw",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "System voltage: 120 V",
      "Load current: 15 A",
      "One-way run length: 100 ft",
      "Wire area (circular mils): 6530"
    ],
    "outputs": [
      "Voltage drop (%): 4.94",
      "Drop (V): 5.93",
      "Voltage at load: 114.1",
      "Verdict: Over 3% — upsize wire"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter system voltage (V).",
      "Enter load current (A).",
      "Enter one-way run length (ft).",
      "Enter wire area (circular mils) — 12 AWG ≈ 6530, 10 AWG ≈ 10380.",
      "Read your voltage drop (%) 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": {
        "volts": 72,
        "amps": 9,
        "length": 60,
        "cm": 3920
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "volts": 120,
        "amps": 15,
        "length": 100,
        "cm": 6530
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "volts": 192,
        "amps": 24,
        "length": 160,
        "cm": 10450
      }
    }
  ],
  "limitations": [
    "Results are rounded for display; the underlying calculation keeps full precision.",
    "Very large or very small inputs may hit floating-point limits in the browser.",
    "Inputs outside the accepted range are clamped rather than rejected."
  ],
  "faq": [
    {
      "q": "How does the wire voltage drop calculator work?",
      "a": "Long runs bleed voltage. Codes generally want branch-circuit drop under 3%. This estimates drop from length, current, and copper wire area. The underlying maths is: Vdrop = 2 × K × I × L ÷ CM (K ≈ 12.9 for copper)"
    },
    {
      "q": "What do I need to enter?",
      "a": "4 values: system voltage, load current, one-way run length, and wire area (circular mils). 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 voltage drop (%) result mean?",
      "a": "It is returned as a decimal 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. Results are rounded for display; the underlying calculation keeps full precision."
    },
    {
      "q": "Who is this tool for?",
      "a": "It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/wire-gauge",
    "https://www.revenuelab.fyi/toolbox/ohms-law"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Voltage Drop Calculator (https://www.revenuelab.fyi/toolbox/voltage-drop)"
}