For dilute gaseous CO₂, the ideal approximation is ρ=PM/(RT). A real-fluid model or compressibility factor is needed as pressure rises or conditions approach phase boundaries.

Enter temperature and absolute pressure, choose an ideal or real-fluid estimate, and inspect density, compressibility context and mass-volume conversions. Presets are useful for STP-style or room-temperature exploration, while pressurized storage requires phase-aware property data.

CO₂ density changes with the definition of “standard” conditions. A value quoted at 0°C and 1 atm is not the same as a value at 25°C and 1 bar. Always include temperature and pressure with a gas density value.

Liquid CO₂ exists only within an appropriate temperature-pressure region. Its density is far higher than gaseous CO₂ and changes with temperature and pressure. Use a validated real-fluid property source for design, charging or safety calculations.

Above the critical point, CO₂ is supercritical. Density can vary rapidly around the critical region even for modest pressure or temperature changes. This is important in supercritical extraction, carbon capture/storage and process design.

The critical region is why a phase diagram is more informative than a single table. Below the triple-point pressure, liquid CO₂ cannot exist. At atmospheric pressure, solid CO₂ sublimes rather than melting into a stable liquid.

Once density at the actual state is known, mass and volume follow from m=ρV and V=m/ρ. Do not reuse the same density after changing pressure or temperature significantly.

At comparable ordinary conditions, CO₂ is denser than dry air and molecular oxygen. That does not mean it behaves as a permanently separated “floor layer” in every real environment; ventilation, turbulence and mixing matter.

The built-in real-fluid estimate is educational and convenient, not a replacement for NIST-quality property software, certified process simulation or pressure-equipment design data. Near phase boundaries, use authoritative thermophysical property models.

At 25°C and about 1 atm, an ideal-gas calculation gives CO₂ density around 1.8 kg/m³. At higher pressure the real-fluid result increasingly departs from the ideal prediction. The calculator displays a compressibility factor so you can see when the simple model is being stretched.

Gas-phase values are typically measured in kg/m³ or g/L, while liquid and supercritical values can reach hundreds of kg/m³. A table that mixes these states without pressure and temperature labels is more decorative than scientific.

CO₂ can create asphyxiation hazards in confined spaces and high-pressure systems have mechanical hazards. Density calculations do not size relief devices, ventilation or pressure vessels. Process work should use certified property data and applicable safety standards.