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Constant-Temperature Gas Pressure, Volume and Amount

Relate absolute pressures and volumes at fixed temperature, preserve unit and inverse controls, and calculate the read-only amount from the initial state.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

At fixed temperature and amount, raising absolute pressure from 100,000 to 200,000 Pa changes 0.01 m³ to 0.005 m³.

p₁V₁ = p₂V₂; p₁V₁ = nRT

Worked example

Enter these known values and leave the other values blank.

Initial pressure (p₁)
100000 Pa
Initial volume (V₁)
0.01 m³
Final pressure (p₂)
200000 Pa
Final volume (V₂)
0.005 m³
Amount of gas
0.4077 mol

Assumptions and limitations

  • Hold temperature and amount constant between the two states. This finite ideal-gas workflow requires positive absolute pressure, volume, Kelvin temperature and amount; it excludes zero and negative absolute states.
  • Temperature entries in Celsius or Fahrenheit are converted to absolute Kelvin before ratios or pV=nRT. Negative Celsius can be valid above −273.15°C. Pressure must be absolute, not an unadjusted gauge reading.
  • Supply three independent pressure/volume state measures to recover the fourth. Temperature is a shared editable known value; the extra initial-state relation n=p₁V₁/(RT) calculates amount in moles as a read-only output. Amount cannot be entered to recover temperature, pressure or volume in this public workflow.
  • The model assumes a fixed amount of ideal gas without leakage or phase change. It does not model condensation, high-density interactions, reaction or changing amount. The retained gas constant is modernized to the exact SI value.
  • The pressure unit inHg uses conventional mercury at 0°C and standard gravity, with 1 inHg = 3386.388640341 Pa; mmHg uses the corresponding 133.322387415 Pa factor. Torr is 101325/760 Pa, which is close but not identical to that mmHg convention.
  • The initial temperature is an editable 295 K default. It is constant between the two states, and can also be inferred through the initial-state ideal-gas equation when cleared. Amount is entered in moles with a fixed mol suffix.

Common questions

What must stay fixed in this two-state law?

Keep temperature and amount fixed. Use absolute temperature and absolute pressure. A different path or a changing gas amount requires a different relation.

Can I use Celsius or Fahrenheit?

Yes. The selected temperature unit is converted to Kelvin before calculation. For example, 0°C means 273.15 K; temperature ratios do not use the displayed Celsius values directly.

What do the additional amount controls do?

It is a read-only estimate in moles from initial absolute pressure, initial volume and the shared positive temperature. It is not an editable mass or amount input.

References

Use the exact SI molar gas constant R = N_A k_B = 8.31446261815324 J/(mol·K), replacing the captured 8.3144598 in the ideal-gas equation and every inverse; the two-state ratio law is unchanged. Mercury pressure columns use conventional density and standard gravity, with the exact international inch. Pounds-force per square inch use the exact international pound and inch with standard gravity, replacing the rounded captured factor. One technical atmosphere is exactly one kilogram-force per square centimeter under standard gravity.

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