{
  "slug": "lightning-distance-calculator",
  "title": "Lightning Distance Calculator",
  "heading": "Lightning Strike Distance Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/lightning-distance-calculator",
  "summary": "Estimate how far away a lightning strike is using the flash-to-bang time delay.",
  "description": "Light travels essentially instantaneously over storm-relevant distances, but sound travels at roughly 1,125 feet per second (about 343 m/s) at typical air temperature, so counting seconds between the lightning flash and the thunder clap gives a direct distance estimate. This is the same 'flash-to-bang' method used by lifeguards, golf courses, and outdoor event operators to decide when to suspend activity — the widely used 30-30 rule says if flash-to-bang is under 30 seconds (storm within about 6 miles), seek shelter immediately, and wait 30 minutes after the last strike before resuming outdoor activity, since lightning has struck as far as 10-12 miles from the parent storm cell.",
  "formula": "Distance (mi) = seconds ÷ 5 (approx); distance (km) = seconds ÷ 3; based on sound speed of ~1,125 ft/s.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=lightning-distance-calculator",
  "inputs": [
    {
      "id": "seconds",
      "label": "Seconds between flash and thunder",
      "kind": "number",
      "hint": null,
      "default": 12,
      "unit": null,
      "min": 0,
      "max": 120
    },
    {
      "id": "tempF",
      "label": "Air temperature (affects sound speed)",
      "kind": "number",
      "hint": null,
      "default": 70,
      "unit": "°F",
      "min": -10,
      "max": 110
    }
  ],
  "outputs": [
    {
      "id": "distanceMi",
      "label": "Estimated distance",
      "format": "decimal",
      "hint": null,
      "primary": true
    },
    {
      "id": "distanceKm",
      "label": "Distance (km)",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "speedFtPerSec",
      "label": "Speed of sound used (ft/s)",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "safety",
      "label": "Safety guidance",
      "format": "raw",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Seconds between flash and thunder: 12",
      "Air temperature (affects sound speed): 70 °F"
    ],
    "outputs": [
      "Estimated distance: 2.57",
      "Distance (km): 4.13",
      "Speed of sound used (ft/s): 1,129",
      "Safety guidance: Danger — seek shelter now"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter seconds between flash and thunder.",
      "Enter air temperature (affects sound speed) (°F).",
      "Read your estimated distance 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": {
        "seconds": 7,
        "tempF": 42
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "seconds": 12,
        "tempF": 70
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "seconds": 19,
        "tempF": 110
      }
    }
  ],
  "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 divide seconds by 5 for miles?",
      "a": "Sound travels roughly 1,125 feet per second at normal temperatures, and there are 5,280 feet in a mile, so 5,280 ÷ 1,125 ≈ 4.7 seconds per mile, commonly rounded to 5 for a quick mental estimate — this calculator uses the more precise temperature-adjusted speed instead of the rounded rule of thumb."
    },
    {
      "q": "What is the 30-30 rule?",
      "a": "If the flash-to-bang count is 30 seconds or less (meaning the storm is within about 6 miles), go indoors immediately. Wait at least 30 minutes after the last observed lightning or thunder before resuming outdoor activities, since storms can produce strikes well ahead of and behind the visible rain core."
    },
    {
      "q": "Can lightning strike without visible rain overhead?",
      "a": "Yes — 'bolts from the blue' can strike 10 miles or more from the parent thunderstorm, sometimes under apparently clear sky, which is exactly why the safety buffer in this calculator and the 30-30 rule extends well beyond where rain is falling."
    },
    {
      "q": "Does air temperature meaningfully change the distance estimate?",
      "a": "Slightly — sound speed increases about 1.1 ft/s per degree Fahrenheit, so on a very hot day sound travels marginally faster than on a cold day, shifting distance estimates by a few percent at most over the ranges relevant to storm safety."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/wind-pressure-on-wall",
    "https://www.revenuelab.fyi/toolbox/wbgt-heat-stress"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Lightning Distance Calculator (https://www.revenuelab.fyi/toolbox/lightning-distance-calculator)"
}