Air Concentration ppm to mg per m³ Calculator

Convert between parts-per-million (ppm) and mass concentration (mg/m³) for gases and vapors in air. Essential for environmental monitoring, industrial hygiene, and lab safety. Supports temperature and pressure corrections, runs 100% offline, and includes verification steps.

Educational only. Follow your lab SOPs and SDS.

Quick Unit Strip

ppm	ppb	µg/m³	mg/m³	g/m³	mol/m³

Table updates live based on current Molecular Weight, Temperature, and Pressure. Values are per 1 ppm of the specified compound.

Understanding ppm to mg/m³ Conversions

This conversion is critical for comparing regulatory limits (often in ppm) with measured mass concentrations (mg/m³ from filters or sensors). The calculation depends on the gas's molecular weight and the ambient conditions because ppm is a volume ratio, while mg/m³ is a mass per volume.

Step-by-Step Usage

Enter concentration in the left field. Use the swap button to change the input unit between ppm and mg/m³.
Provide the molecular weight of the gas or vapor in g/mol. For air (approximate average), use 28.97 g/mol.
Set temperature and pressure of the air sample. The calculator automatically corrects the molar volume. Use the STP/NTP buttons for standard conditions.
View the result in the right panel, along with intermediate values (molar volume, air density) for verification.
Check the unit strip for a broader view of equivalent concentrations across common units.

Realistic Examples

Scenario	Input (ppm)	MW (g/mol)	Conditions	Result (mg/m³)
CO OSHA PEL	50	28.01	NTP	57.2
Toluene TWA	20	92.14	25°C, 1 atm	75.3
High-altitude CO₂	400	44.01	0°C, 0.7 atm	786.5

Common Mistakes Checklist

Using the wrong molecular weight (e.g., for a mixture instead of the target compound).
Forgetting to adjust temperature and pressure for non‑standard conditions.
Confusing ppm by volume (gas) with ppm by mass (aqueous). This tool is for gases in air.
Using mg/m³ values without noting the reference conditions, making comparisons invalid.
Not verifying that extreme temperatures or pressures invalidate the ideal‑gas assumption.

Frequently Asked Questions

What are the accuracy limits of this conversion?

The calculation assumes ideal‑gas behavior. Accuracy is typically within 1% for common gases near room temperature and pressure. For polar gases, high pressures (>5 atm), or near condensation points, deviations increase.

When does the ppm to mg/m³ relationship change?

The ratio changes with temperature and pressure because the molar volume of air changes. Always specify the conditions when reporting mg/m³. Regulatory limits are often referenced to 25°C and 1 atm (NTP).

What is the difference between STP and NTP?

STP (Standard Temperature and Pressure) is 0°C and 1 atm, giving a molar volume of 22.414 L/mol. NTP (Normal Temperature and Pressure) is 25°C and 1 atm, giving 24.465 L/mol. Industrial hygiene commonly uses NTP.

How do I measure molecular weight for a mixture?

For a known mixture, compute the average molecular weight: MW_avg = Σ (mole_fraction_i × MW_i). For unknown mixtures, direct measurement (e.g., GC‑MS) is needed. Using air's average MW (28.97) is only valid for trace contaminants in air.

Formulas & Assumptions

Main formula: C_mg_per_m3 = (C_ppm × MW) / V_m where V_m is the molar volume (L/mol) at sample conditions.

Molar volume: V_m = (R × T) / P, with R = 0.08205746 L·atm/(mol·K), T in Kelvin, P in atm.

Temperature conversion: K = °C + 273.15; K = (°F − 32) × 5/9 + 273.15.

Pressure conversion factors: 1 atm = 1.01325 bar = 101.325 kPa = 760 torr.

Rounding: Results are rounded to the selected decimal places; intermediate values use full precision.

Assumptions: Ideal gas law applies; the gas mixture is dilute (trace component in air).

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Air Concentration ppm to mg per m3

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