STP / NTP Gas Volume Unit Converter
Convert a gas volume from one set of conditions (STP, IUPAC STP, NTP, SATP, or custom temperature and pressure) to another using the combined gas law, and convert freely between mL, L, m³, cm³, ft³, in³, and US gallons/quarts.
Source conditions (where V1 was measured)
Target conditions (convert V1 to here)
Gas Volume Conversion Diagram
The same amount of gas (same n), shown at its source conditions on the left and its converted conditions on the right.
Step-by-Step Solution
Here's exactly how this answer was calculated, one step at a time.
Given: V1 = 22.4 L at T1 = 273.15 K, P1 = 1 atm → T2 = 293.15 K, P2 = 1 atm
Step 1: Convert everything to consistent units
The combined gas law needs volume in a single consistent unit and both temperatures in kelvin, so every input is converted to litres, kelvin, and atmospheres first.
V1 = 22.4 L, T1 = 273.15 K, P1 = 1 atm, T2 = 293.15 K, P2 = 1 atmStep 2: Find the moles of gas from the source conditions
The amount of gas (moles) doesn't change when conditions change, so it's calculated once from the source volume, temperature, and pressure using the ideal gas law.
n = (P1 × V1) ÷ (R × T1) = (1 × 22.4) ÷ (0.08206 × 273.15) = 0.999377 molStep 3: Write the combined gas law
Because the same amount of gas is being compared under two different conditions, PV/T stays constant — this is the combined gas law, and it's equivalent to solving PV = nRT twice for the same n.
P1V1 / T1 = P2V2 / T2Step 4: Solve for the new volume
This rearrangement gives the new volume directly, without needing to calculate moles separately, though the mole count found above must stay the same for both conditions.
V2 = (P1 × V1 × T2) ÷ (P2 × T1) = (1 × 22.4 × 293.15) ÷ (1 × 273.15) = 24.04012 LStep 5: Convert to your chosen output unit
The final volume in litres is converted into whichever unit you selected for the result.
V2 = 24.04012 L = 24.04012 L
The converted gas volume is:
24.04012 L
Free STP / NTP Gas Volume Unit Converter
This converter finds the volume a gas would occupy under a different set of conditions than the ones it was measured at, using the combined gas law. It's built specifically around the standard reference conditions used in chemistry — STP, IUPAC STP, NTP, and SATP — with one-click buttons for each, plus a full custom option for any temperature and pressure you need.
It also converts between the common volume units chemistry problems use: millilitres, litres, cubic metres, cubic centimetres, cubic feet, cubic inches, and US gallons/quarts, so you can move between metric and imperial units at the same time as changing the reference conditions.
STP, IUPAC STP, NTP, and SATP — What's the Difference?
'Standard' gas conditions are not as standard as the name suggests. Classic STP (Standard Temperature and Pressure) is 0°C and exactly 1 atm, and it's the definition most general chemistry textbooks and exams still use — it gives the well-known molar volume of about 22.4 L/mol. The IUPAC definition of STP instead uses 0°C and exactly 100 kPa, a very slightly lower pressure than 1 atm, which shifts the molar volume to about 22.7 L/mol.
NTP (Normal Temperature and Pressure) is typically 20°C and 1 atm — closer to a comfortable lab bench temperature — and is common in engineering and industrial gas contexts. SATP (Standard Ambient Temperature and Pressure), sometimes just called 'room temperature and pressure', is usually taken as 25°C and 1 atm. Because these definitions genuinely conflict with each other, always check which one a specific textbook, exam, or standard is using before comparing results.
The Combined Gas Law: P1V1/T1 = P2V2/T2
Converting a gas volume between two different sets of conditions uses the combined gas law, P1V1/T1 = P2V2/T2, which holds for a fixed amount of gas (fixed number of moles). Rearranged for the new volume, this becomes V2 = P1V1T2/(P2T1) — exactly what this converter calculates for you after making sure every temperature is in kelvin and every pressure is in a matching unit.
Behind the scenes, the converter also calculates the number of moles from the source conditions using PV = nRT, so it can double-check the new volume by solving forward from moles rather than only rearranging the combined gas law — both routes give the same answer for an ideal gas.
Worked Example: Converting a Volume from STP to NTP
Suppose a reaction produces 22.4 L of gas measured at classic STP (0°C, 1 atm), and you want to know what volume that same amount of gas would occupy at NTP (20°C, 1 atm) instead. Since pressure is unchanged, only the temperature ratio matters: V2 = V1 × (T2/T1) = 22.4 × (293.15/273.15) ≈ 24.05 L.
This kind of conversion comes up constantly in gas stoichiometry problems, where a reaction's gas product is measured under lab conditions but needs to be compared against a textbook value quoted at STP, or vice versa.
Molar Volume: How Much Space One Mole of Gas Takes Up
Molar volume, Vm = RT/P, is the volume that exactly one mole of an ideal gas occupies at a given temperature and pressure — this converter shows it for both your source and target conditions. At classic STP this works out to about 22.414 L/mol; at IUPAC STP, about 22.711 L/mol; at NTP, about 24.055 L/mol; and at SATP, about 24.465 L/mol.
Because molar volume is the same for any ideal gas at a given temperature and pressure (regardless of molar mass), it's one of the most useful shortcut numbers in general chemistry — multiply it by moles to get volume, or divide a measured volume by it to get moles, without ever needing to know the identity of the gas.
Why Gas Volume Depends on Conditions (Unlike Solids and Liquids)
Solids and liquids are nearly incompressible, so their volume barely changes with pressure or temperature. Gases are the opposite: because gas molecules are spread far apart with mostly empty space between them, squeezing (raising pressure) or expanding (raising temperature) a gas changes its volume dramatically, which is exactly what the combined gas law describes.
This is why a gas volume is meaningless without also stating the conditions it was measured at — '2 litres of oxygen' tells you nothing about how many moles that is unless you also know the temperature and pressure, which is the whole reason standard conditions like STP and NTP exist in the first place.
STP/NTP Gas Volume Converter: Quick Reference
V2 = P1V1T2/(P2T1), always with both temperatures in kelvin and both pressures in the same unit. Classic STP is 0°C/1 atm (Vm ≈ 22.4 L/mol), IUPAC STP is 0°C/100 kPa (Vm ≈ 22.7 L/mol), NTP is 20°C/1 atm (Vm ≈ 24.1 L/mol), and SATP is 25°C/1 atm (Vm ≈ 24.5 L/mol).
This converter is built for educational and lab-planning use with ideal-gas assumptions; for gases under high pressure or near condensation, a real-gas equation like Van der Waals will give a more accurate volume than this ideal conversion.
Frequently Asked Questions
What is the difference between STP and NTP?
Classic STP is 0°C and 1 atm. NTP (Normal Temperature and Pressure) is 20°C and 1 atm — a higher, more room-like temperature than STP, which changes the resulting gas volume.
What is IUPAC STP?
IUPAC's modern definition of STP uses 0°C and exactly 100 kPa, which is very slightly lower pressure than the classic 1 atm STP definition, giving a molar volume of about 22.7 L/mol instead of 22.4 L/mol.
How do I convert a gas volume from one condition to another?
Use the combined gas law: V2 = P1V1T2/(P2T1), with both temperatures in kelvin and both pressures in matching units. This converter does that calculation automatically.
What is molar volume?
Molar volume (Vm = RT/P) is the volume one mole of an ideal gas occupies at a given temperature and pressure — about 22.4 L/mol at classic STP for any ideal gas, regardless of its identity.
Why does a gas volume change with temperature and pressure but a liquid's doesn't?
Gas molecules are spread far apart with mostly empty space between them, so changing temperature or pressure changes that spacing dramatically. Liquids and solids are nearly incompressible by comparison.
What is SATP?
SATP (Standard Ambient Temperature and Pressure), also called room temperature and pressure, is usually defined as 25°C and 1 atm.
Can I convert between volume units without changing conditions?
Yes — set the source and target temperature and pressure to the same values, and the converter will simply convert your volume between units like mL, L, m³, ft³, and US gallons.
Does this converter work for real (non-ideal) gases?
It uses the ideal gas law, which is an excellent approximation for most gases at everyday pressures and temperatures. Near condensation or at very high pressure, a real-gas equation will be more accurate.