CO2 Equivalent Units Calculation Indoor Air Quality Calculator

Calculator Input

Space Name

Known CO2 Value

Known Unit

Outdoor CO2 Baseline (ppm)

Occupants

Room Volume (m³)

Air Temperature (°C)

Pressure (kPa)

CO2 Generation Rate (L/s/person)

Target Indoor CO2 (ppm)

Molecular Weight (g/mol)

Reset

The layout remains single-column overall, while inputs use 3 columns on large screens, 2 on smaller screens, and 1 on mobile.

Formula Used

1) ppm to mg/m³
mg/m³ = ppm × MW × Pressure(kPa) ÷ [R × Temperature(K)]

2) mg/m³ to ppm
ppm = mg/m³ × R × Temperature(K) ÷ [MW × Pressure(kPa)]

3) Volume Percent
Volume % = ppm ÷ 10,000

4) Mole Fraction
Mole Fraction = ppm ÷ 1,000,000

5) Excess Indoor CO2
Excess ppm = Indoor ppm − Outdoor ppm

6) Estimated Fresh Air per Person
Fresh Air (L/s/person) = CO2 Generation Rate × 1,000,000 ÷ Excess ppm

7) Air Changes per Hour
ACH = [Total Fresh Air (L/s) × 3.6] ÷ Room Volume(m³)

These equations combine ideal gas relationships with a simple steady-state ventilation model. They are useful for screening indoor air conditions, unit conversions, and approximate ventilation checks.

How to Use This Calculator

Enter your known CO2 reading and choose its unit.
Set the outdoor baseline, room volume, and number of occupants.
Provide temperature and pressure for accurate mass conversion.
Enter a per-person CO2 generation rate suitable for the activity level.
Set your target indoor CO2 concentration.
Click Calculate Now to display results above the form.
Review converted units, ventilation estimates, room mass, and ACH.
Use the CSV or PDF buttons to save the calculated summary.

Example Data Table

Scenario	Indoor CO2 (ppm)	Outdoor CO2 (ppm)	Occupants	Fresh Air (L/s/person)	ACH	Interpretation
Open Office	950	420	8	9.81	1.57	Good
Small Meeting Room	1,350	430	6	5.65	2.03	Moderate
Classroom	1,850	420	25	3.64	2.73	Poor

Frequently Asked Questions

1) What does CO2 equivalent units calculation mean here?

It means converting a known CO2 reading into equivalent concentration units such as ppm, mg/m³, µg/m³, volume percent, and mole fraction, then using that value for ventilation and indoor air quality interpretation.

2) Why is outdoor CO2 needed?

Outdoor CO2 provides the background reference. Indoor excess above that baseline is what supports approximate ventilation calculations using steady-state mass balance logic.

3) Is the ventilation result exact?

No. It is an estimate based on steady conditions, assumed generation rates, and reasonably mixed indoor air. Real buildings can behave differently because of varying occupancy, air distribution, and system performance.

4) What unit should I enter from a sensor?

Most indoor air sensors report CO2 in ppm. If your instrument reports mass concentration or another unit, choose that unit first and the calculator will convert it before estimating ventilation metrics.

5) Why are temperature and pressure included?

Mass-based conversions depend on air state. Changing temperature or pressure changes gas density, so ppm to mg/m³ conversion becomes more accurate when those conditions are included.

6) What is a typical target indoor CO2 value?

Many users choose 800 to 1,000 ppm for screening comfort and ventilation. Actual project limits should follow the standard, policy, or design brief that applies to the building.

7) What does ACH tell me?

ACH shows how many room volumes of supply air are delivered each hour. It is useful for comparing spaces, but it should be reviewed together with occupancy and outdoor air requirements.

8) Can I use this for compliance reporting?

Use it for screening, planning, and preliminary review. Formal compliance decisions should rely on site measurements, approved methods, and the exact code or standard governing the project.