{
  "id": "tire-pressure",
  "version": "a0e23d3fbc50",
  "status": "published",
  "name": "Tire Pressure Calculator",
  "question": "What is my tire pressure?",
  "summary": "Works out a tire’s pressure at a new temperature from its gauge pressure at another temperature (Gay-Lussac’s law with absolute pressure), or the cold pressure to set, in psi, kPa or bar.",
  "category": "everyday-life",
  "subcategory": "travel-and-fuel",
  "url": "https://www.acalculator.org/everyday-life/tire-pressure-calculator",
  "markdown": "https://www.acalculator.org/everyday-life/tire-pressure-calculator.md",
  "kind": "formulas",
  "method": "(P₁ + 1 atm) ÷ T₁ = (P₂ + 1 atm) ÷ T₂, with gauge pressures P and absolute temperatures T; P₂ = (P₁ + 1 atm) × T₂ ÷ T₁ − 1 atm.",
  "assumptions": [
    "The tire’s volume and the amount of air in it stay the same; no air leaks out or is added.",
    "The air around the tire is at 1 standard atmosphere (101.325 kPa, 14.696 psi), which a gauge does not count.",
    "Temperatures convert to kelvins: (°F + 459.67) × 5/9, °C + 273.15."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "p1": {
        "title": "Tire pressure now",
        "description": "The gauge reading at the first temperature.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "pressure",
        "minimum": 0,
        "maximum": 2000000
      },
      "t1": {
        "title": "Temperature now",
        "description": "The temperature of the tire (or the air around a parked tire) at that reading.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "temperature",
        "minimum": 173.15,
        "maximum": 473.15
      },
      "p2": {
        "title": "Tire pressure then",
        "description": "The gauge reading at the second temperature.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "pressure",
        "minimum": 0,
        "maximum": 2000000
      },
      "t2": {
        "title": "Temperature then",
        "description": "The second temperature of the tire.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "temperature",
        "minimum": 173.15,
        "maximum": 473.15
      }
    }
  },
  "solve": {
    "fillAny": 3,
    "variables": [
      "p1",
      "t1",
      "p2",
      "t2"
    ],
    "inputsOnly": []
  },
  "outputs": {
    "p1": {
      "label": "Tire pressure now",
      "description": "The gauge reading at the first temperature.",
      "format": "quantity"
    },
    "t1": {
      "label": "Temperature now",
      "description": "The temperature of the tire (or the air around a parked tire) at that reading.",
      "format": "quantity"
    },
    "p2": {
      "label": "Tire pressure then",
      "description": "The gauge reading at the second temperature.",
      "format": "quantity"
    },
    "t2": {
      "label": "Temperature then",
      "description": "The second temperature of the tire.",
      "format": "quantity"
    },
    "change": {
      "label": "Change in pressure",
      "description": "The second gauge reading minus the first.",
      "format": "quantity",
      "unit": "psi"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "p1": 241316.50526089262,
      "t1": 294.2611111111112,
      "t2": 272.0388888888889
    },
    "outputs": {
      "p2": 215440.65763796563,
      "change": -25875.847622926987
    },
    "text": "A tire at 35 psi and 70 °F reads 31.25 psi at 30 °F."
  },
  "examples": [
    {
      "given": {
        "p1": 241316.50526089262,
        "t1": 294.2611111111112,
        "t2": 272.0388888888889
      },
      "expect": {
        "p2": 215440.65763796563,
        "change": -25875.847622926987
      },
      "source": "hand calculation in content.mdx: (35 + 14.696) × 489.67 ÷ 529.67 − 14.696 = 31.25 psi; OpenStax, Chemistry 2e, §9.2 (Amontons’s or Gay-Lussac’s law: P₁/T₁ = P₂/T₂ at constant volume), https://openstax.org/books/chemistry-2e/pages/9-2-relating-pressure-volume-amount-and-temperature-the-ideal-gas-law; NIST SP 811 Appendix B.9 (1 atm = 101,325 Pa; 1 psi = 6,894.757 Pa), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9"
    },
    {
      "given": {
        "p1": 240000,
        "t1": 293.15,
        "t2": 333.15
      },
      "expect": {
        "p2": 286573.4265734266
      },
      "source": "hand calculation in content.mdx: (240 + 101.325) × 333.15 ÷ 293.15 − 101.325 = 286.57 kPa; OpenStax, Chemistry 2e, §9.2 (Amontons’s or Gay-Lussac’s law: P₁/T₁ = P₂/T₂ at constant volume), https://openstax.org/books/chemistry-2e/pages/9-2-relating-pressure-volume-amount-and-temperature-the-ideal-gas-law"
    },
    {
      "given": {
        "p2": 248211.262554061,
        "t1": 293.15000000000003,
        "t2": 308.15000000000003
      },
      "expect": {
        "p1": 231196.6789476651
      },
      "source": "hand calculation in content.mdx: (36 + 14.696) × 527.67 ÷ 554.67 − 14.696 = 33.53 psi; OpenStax, Chemistry 2e, §9.2 (Amontons’s or Gay-Lussac’s law: P₁/T₁ = P₂/T₂ at constant volume), https://openstax.org/books/chemistry-2e/pages/9-2-relating-pressure-volume-amount-and-temperature-the-ideal-gas-law; NIST SP 811 Appendix B.9 (1 atm = 101,325 Pa; 1 psi = 6,894.757 Pa), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9"
    },
    {
      "given": {
        "p1": 220632.23338138754,
        "t1": 297.03888888888895,
        "p2": 193053.2042087141
      },
      "expect": {
        "t2": 271.5943784610678
      },
      "source": "hand calculation in content.mdx: 534.67 × (28 + 14.696) ÷ (32 + 14.696) = 488.87 °R = 29.2 °F; OpenStax, Chemistry 2e, §9.2 (Amontons’s or Gay-Lussac’s law: P₁/T₁ = P₂/T₂ at constant volume), https://openstax.org/books/chemistry-2e/pages/9-2-relating-pressure-volume-amount-and-temperature-the-ideal-gas-law; NIST SP 811 Appendix B.9 (1 atm = 101,325 Pa; 1 psi = 6,894.757 Pa), https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9"
    }
  ],
  "sources": [
    "OpenStax, Chemistry 2e, section 9.2: at constant volume and amount, the pressure of a gas is proportional to its absolute temperature (Amontons’s or Gay-Lussac’s law, P₁/T₁ = P₂/T₂). CC BY 4.0, retrieved 2026-10-02. https://openstax.org/books/chemistry-2e/pages/9-2-relating-pressure-volume-amount-and-temperature-the-ideal-gas-law",
    "NIST Special Publication 811, Appendix B.9: 1 standard atmosphere = 101,325 Pa exactly; 1 psi = 6,894.757 Pa. Retrieved 2026-10-02. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9"
  ],
  "related": [
    "tire-size",
    "gas-mileage",
    "combined-gas-law"
  ],
  "changelog": []
}