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STP Calculator

Chemistry

Convert gas volume between STP (0°C, 1 atm) and any temperature/pressure using the ideal gas law. Calculate molar volume and moles of gas at standard conditions.

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Volume at STP (L)

22.414
Volume at Given T,P (L)
22.414
Molar Volume at STP (L/mol)
22.414

This calculator computes your Volume at STP (L), Volume at Given T,P (L), Molar Volume at STP (L/mol) from the values you enter.

Inputs
Moles of Gas (mol)Temperature (°C)Pressure (atm)
Outputs
Volume at STP (L)Volume at Given T,P (L)Molar Volume at STP (L/mol)

What is a STP?

The STP Calculator computes the volume of a gas at Standard Temperature and Pressure (STP: 0°C, 1 atm) and at any other temperature and pressure, using the ideal gas law PV = nRT. Enter the number of moles, the operating temperature in °C, and the pressure in atm to get the STP volume, the volume at given conditions, and the molar volume at STP.

STP (Standard Temperature and Pressure) — 0°C and 1 atm — is the universal reference condition for comparing and reporting gas volumes. At STP, one mole of any ideal gas occupies 22.414 L (the standard molar volume). This single fact simplifies dozens of stoichiometry problems: 22.4 L of hydrogen at STP contains exactly 1 mole of H₂; 22.4 L of any gas mixture at STP contains exactly 1 mole of gas molecules.

The ideal gas law PV = nRT with R = 0.082057 L·atm/(mol·K) allows conversion between any two sets of conditions. This calculator computes both the STP volume (using T = 273.15 K, P = 1 atm) and the volume at any other (T, P) from the entered mole count, supporting both "find STP volume" and "find volume at other conditions" use cases in a single calculation.

For gas calculations involving mixtures, see the Partial Pressure Calculator. For molar mass from gas density at STP, see the Molar Mass of Gas Calculator.

How to use this STP calculator

  1. Enter the Moles of Gas in the first field — this is the amount of gas you have or are working with.
  2. Enter the actual Temperature in °C for the "at given conditions" volume output. For STP volume only, this can be left at 0°C.
  3. Enter the actual Pressure in atm for the "at given conditions" volume output. For STP volume only, leave at 1 atm.
  4. Read Volume at STP (L) = n × 22.414 L.
  5. Use Volume at Given T, P for the actual operating conditions, or to verify the combined gas law conversion.

Formula & Methodology

Ideal gas law:

PV = nRT V = nRT / P R = 0.082057 L·atm/(mol·K)

STP volume:

V_STP = n × R × T_STP / P_STP        = n × 0.082057 × 273.15 / 1        = n × 22.414 L

Combined gas law (STP ↔ other conditions):

V₂ = V₁ × (P₁/P₂) × (T₂/T₁)    = V_STP × (1/P) × (T/273.15)

Worked example — stoichiometry problem:

2 mol of CO₂ is produced in a combustion reaction. What volume does it occupy at STP, and at 25°C and 0.9 atm?

V_STP = 2 × 22.414 = 44.83 L  V(25°C, 0.9 atm) = (2 × 0.082057 × 298.15) / 0.9                  = 48.93 / 0.9                  = 54.37 L

The gas expands from 44.83 L at STP to 54.37 L at room temperature and slightly reduced pressure — a factor of 1.21, consistent with (298.15/273.15) × (1/0.9) = 1.09 × 1.11 = 1.21.

Frequently Asked Questions

STP stands for Standard Temperature and Pressure. The IUPAC definition is 0°C (273.15 K) and 100 kPa (approximately 0.987 atm). An older definition, still widely used in US textbooks and many Indian chemistry curricula, defines STP as 0°C and 1 atm (101.325 kPa). At IUPAC STP, one mole of ideal gas occupies 22.711 L; at the older 1 atm STP, it occupies 22.414 L. Always check which STP definition your textbook or problem uses.
At the older STP definition (0°C, 1 atm), one mole of ideal gas occupies 22.414 L — this is the molar volume. This value, often called the 'standard molar volume', is used directly in gas law calculations and unit conversions. At IUPAC STP (0°C, 100 kPa), the molar volume is 22.711 L/mol. NCERT Class 11 typically uses the older 22.4 L/mol value, which is the most commonly tested figure in Indian board and competitive examinations.
The ideal gas law is PV = nRT, where P is pressure (atm), V is volume (L), n is moles, R is the gas constant (0.082057 L·atm/mol·K), and T is temperature in Kelvin. At STP (T = 273.15 K, P = 1 atm): V = nRT/P = n × 0.082057 × 273.15 / 1 = n × 22.414 L. This shows that 1 mole always gives 22.414 L at STP, regardless of the identity of the gas.
Use the combined gas law: P₁V₁/T₁ = P₂V₂/T₂, rearranged as V₂ = V₁ × (P₁/P₂) × (T₂/T₁). Where V₁ is volume at STP (P₁ = 1 atm, T₁ = 273.15 K), and V₂ is the volume at the target conditions P₂ and T₂. This calculator computes both the STP volume and the volume at any other temperature and pressure from the mole count.
Enter the number of moles of gas, the temperature in °C, and the pressure in atm. The calculator returns: (1) Volume at STP (0°C, 1 atm) using V = n × 22.414 L, (2) Volume at the entered temperature and pressure using PV = nRT, and (3) the molar volume at STP (always 22.414 L/mol for an ideal gas).
STP (Standard Temperature and Pressure) is 0°C (273.15 K) and 1 atm (older) or 100 kPa (IUPAC). SATP (Standard Ambient Temperature and Pressure) is 25°C (298.15 K) and 100 kPa. At SATP, one mole of ideal gas occupies 24.790 L — larger than at STP because the higher temperature expands the gas. SATP is used for thermodynamic standard state values (ΔH°, ΔG°, S°), while STP is used for gas volume calculations. The two are sometimes confused, so it is important to know which standard the problem uses.
The ideal gas law assumes no intermolecular forces and zero molecular volume. Real gases deviate because: (1) attractive forces between molecules reduce pressure slightly (molecules are 'pulled back'); (2) molecular volume is non-zero (reducing available space). At STP, the deviations are small for most gases: N₂ occupies 22.40 L/mol (vs. 22.414 L ideal), O₂ occupies 22.39 L/mol. CO₂, with stronger intermolecular forces, deviates more: 22.26 L/mol. High pressure and low temperature increase deviations.
No — standard state for thermodynamic quantities (ΔH°, ΔG°, S°) uses 25°C (298.15 K) and 1 bar (100 kPa), not 0°C and 1 atm. Standard molar entropies S° and standard Gibbs free energies ΔG° are tabulated at 298 K, not at STP. For gas volumes, use STP (0°C, 1 atm or IUPAC 100 kPa); for thermodynamic properties, use 25°C standard state. The confusion between these two 'standard' conditions is one of the most common errors in thermochemistry problems.
Industrial gas specifications in India often state flow rates and quantities at NTP (Normal Temperature and Pressure, 20°C and 1 atm) or at STP. Oxygen for medical use (hospitals, industrial welding) is specified by volume at STP. Acetylene cylinders for gas welding are measured by mass (because acetylene is dissolved in acetone). CNG (compressed natural gas) for vehicles is typically compressed to 200 bar, and its equivalent volume at atmospheric pressure is stated at NTP in m³. The [Partial Pressure Calculator](/partial-pressure-calculator/) handles multi-component gas mixtures.
From volume at STP to mass: moles = volume (L) / 22.414 L/mol; mass = moles × molar mass (g/mol). For example, 44.8 L of CO₂ at STP = 44.8/22.4 = 2 mol; mass = 2 × 44 = 88 g. Conversely, from mass to volume: moles = mass / molar mass; volume at STP = moles × 22.414 L. These conversions are among the most frequently tested calculations in Indian board examinations and JEE preparation.