{
  "id": "timer-555",
  "slug": "555-timer-calculator",
  "url": "https://electronics.tools/tools/555-timer-calculator/",
  "name": "555 Timer Calculator",
  "group": "amp-timing",
  "summary": "Uses exact ln(2), not 0.693. With R1 = 10 kΩ, R2 = 47 kΩ and 10 nF, f is 1.387 kHz.",
  "formulas": [
    {
      "id": "th",
      "label": "Astable high time",
      "plain": "tH = ln(2)·(R1+R2)C",
      "mathml": "<math display=\"block\" xmlns=\"http://www.w3.org/1998/Math/MathML\" aria-label=\"tH = ln(2)·(R1+R2)C\"><mrow><msub><mi>t</mi><mi>H</mi></msub><mo>=</mo><mi>ln</mi><mn>2</mn><mo>⋅</mo><mrow><mo>(</mo><mrow><msub><mi>R</mi><mn>1</mn></msub><mo>+</mo><msub><mi>R</mi><mn>2</mn></msub></mrow><mo>)</mo></mrow><mi>C</mi></mrow></math>",
      "symbols": [
        "R1",
        "R2",
        "C"
      ],
      "sources": [
        "ti"
      ]
    },
    {
      "id": "f",
      "label": "Astable frequency",
      "plain": "f = 1 / (ln(2)·(R1+2 R2)C)",
      "mathml": "<math display=\"block\" xmlns=\"http://www.w3.org/1998/Math/MathML\" aria-label=\"f = 1 / (ln(2)·(R1+2 R2)C)\"><mrow><mi>f</mi><mo>=</mo><mfrac><mn>1</mn><mrow><mi>ln</mi><mn>2</mn><mo>⋅</mo><mrow><mo>(</mo><mrow><msub><mi>R</mi><mn>1</mn></msub><mo>+</mo><mn>2</mn><msub><mi>R</mi><mn>2</mn></msub></mrow><mo>)</mo></mrow><mi>C</mi></mrow></mfrac></mrow></math>",
      "symbols": [
        "R1",
        "R2",
        "C"
      ],
      "sources": [
        "ti"
      ]
    },
    {
      "id": "mono",
      "label": "Monostable pulse",
      "plain": "T = ln(3)·R C (1.1 RC is a labelled approximation)",
      "mathml": "<math display=\"block\" xmlns=\"http://www.w3.org/1998/Math/MathML\" aria-label=\"T = ln(3)·R C (1.1 RC is a labelled approximation)\"><mrow><mi>T</mi><mo>=</mo><mi>ln</mi><mn>3</mn><mo>⋅</mo><mi>R</mi><mi>C</mi></mrow></math>",
      "symbols": [
        "R",
        "C"
      ],
      "sources": [
        "ti"
      ]
    }
  ],
  "variables": [
    {
      "symbol": "mode",
      "name": "Mode",
      "unit": "1",
      "role": "input",
      "precision": {
        "sig": 1
      },
      "default": "astable",
      "urlParam": "mode"
    },
    {
      "symbol": "R1",
      "name": "Astable RA",
      "unit": "Ω",
      "role": "input",
      "precision": {
        "sig": 4
      },
      "range": {
        "min": 0,
        "softMin": 1000,
        "note": "R1 cannot be 0"
      },
      "default": 10000,
      "urlParam": "r1"
    },
    {
      "symbol": "R2",
      "name": "Astable RB",
      "unit": "Ω",
      "role": "input",
      "precision": {
        "sig": 4
      },
      "range": {
        "min": 0,
        "softMin": 1000
      },
      "default": 47000,
      "urlParam": "r2"
    },
    {
      "symbol": "C",
      "name": "Timing capacitor",
      "unit": "F",
      "role": "input",
      "precision": {
        "sig": 4
      },
      "range": {
        "min": 0,
        "softMin": 1e-10,
        "note": "C below ~100 pF meets parasitics"
      },
      "default": 1e-8,
      "urlParam": "c"
    },
    {
      "symbol": "R",
      "name": "Monostable timing resistor",
      "unit": "Ω",
      "role": "input",
      "precision": {
        "sig": 4
      },
      "range": {
        "min": 0
      },
      "default": 100000,
      "urlParam": "r"
    },
    {
      "symbol": "f",
      "name": "Frequency",
      "unit": "Hz",
      "role": "output",
      "precision": {
        "sig": 4
      }
    },
    {
      "symbol": "D",
      "name": "Duty cycle",
      "unit": "%",
      "role": "output",
      "precision": {
        "sig": 4
      }
    }
  ],
  "examples": [
    {
      "id": "10k-47k-10n",
      "title": "Astable 10 kΩ / 47 kΩ / 10 nF",
      "input": [
        {
          "symbol": "mode",
          "value": "astable",
          "unit": "1",
          "display": "astable"
        },
        {
          "symbol": "R1",
          "value": 10000,
          "unit": "Ω",
          "display": "10 kΩ"
        },
        {
          "symbol": "R2",
          "value": 47000,
          "unit": "Ω",
          "display": "47 kΩ"
        },
        {
          "symbol": "C",
          "value": 1e-8,
          "unit": "F",
          "display": "10 nF"
        }
      ],
      "output": [
        {
          "symbol": "f",
          "value": 1387.2067700855416,
          "unit": "Hz",
          "display": "1.387 kHz"
        },
        {
          "symbol": "D",
          "value": 54.807692307692314,
          "unit": "%",
          "display": "54.81 %"
        }
      ],
      "computedBy": "timer555"
    },
    {
      "id": "1k-10k-10u",
      "title": "Astable 1 kΩ / 10 kΩ / 10 µF",
      "input": [
        {
          "symbol": "mode",
          "value": "astable",
          "unit": "1",
          "display": "astable"
        },
        {
          "symbol": "R1",
          "value": 1000,
          "unit": "Ω",
          "display": "1 kΩ"
        },
        {
          "symbol": "R2",
          "value": 10000,
          "unit": "Ω",
          "display": "10 kΩ"
        },
        {
          "symbol": "C",
          "value": 0.00001,
          "unit": "F",
          "display": "10 µF"
        }
      ],
      "output": [
        {
          "symbol": "f",
          "value": 6.86997638518554,
          "unit": "Hz",
          "display": "6.87 Hz"
        },
        {
          "symbol": "D",
          "value": 52.38095238095239,
          "unit": "%",
          "display": "52.38 %"
        }
      ],
      "computedBy": "timer555"
    }
  ],
  "sources": [
    {
      "title": "TI NE555 datasheet (SLFS022)",
      "url": "https://www.ti.com/lit/ds/symlink/ne555.pdf",
      "retrieved": "2026-11-02",
      "standard": "SLFS022"
    }
  ],
  "datePublished": "2026-11-02T00:00:00+08:00",
  "dateModified": "2026-11-02T00:00:00+08:00",
  "author": {
    "name": "Jasper",
    "url": "https://electronics.tools/about/#jasper"
  },
  "relatedTools": [
    "https://electronics.tools/tools/rc-time-constant-calculator/",
    "https://electronics.tools/tools/capacitor-calculator/",
    "https://electronics.tools/tools/op-amp-gain-calculator/",
    "https://electronics.tools/tools/inverting-op-amp-calculator/"
  ],
  "relatedParts": [
    "https://electronics.tools/parts/ti/ne555p/"
  ]
}