Enter the dew point temperature and total pressure into the calculator to determine the approximate water vapor concentration in ppm by volume (ppmv).
Quick overview: Dew Point to PPM
For a gas mixture at total pressure ptotal, the dew point identifies the temperature where water vapor becomes saturated. At that temperature, the water partial pressure equals the saturation vapor pressure. The volume mixing ratio is then estimated by ppm(v) ≈ 10⁶ × pH₂O / ptotal.
- At 0 °C and 1 atm: psat ≈ 0.61 kPa → ≈ 6,000 ppm
- At 10 °C and 1 atm: psat ≈ 1.23 kPa → ≈ 12,000 ppm
- At 20 °C and 1 atm: psat ≈ 2.34 kPa → ≈ 23,000 ppm
- At 30 °C and 1 atm: psat ≈ 4.25 kPa → ≈ 42,000 ppm
The calculator uses a Magnus-type empirical equation for saturation vapor pressure over liquid water and then converts that partial pressure into ppm(v) using the entered total pressure.
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Dew Point to PPM Formula
The following formulas are used to calculate the approximate water vapor concentration in ppm(v) from dew point and total pressure.
p_{sat}(T_d) = 6.112 \times e^{\frac{17.62T_d}{243.12 + T_d}}PPM(v) \approx 10^6 \times \frac{p_{sat}}{p_{total}}Variables:
- psat is the saturation vapor pressure of water at the dew point
- Td is the dew point temperature in °C
- ptotal is the total gas pressure in kPa
- PPM(v) is the approximate water vapor concentration in parts per million by volume
To calculate ppm(v), first determine the saturation vapor pressure of water at the dew point, then divide that pressure by the total pressure and multiply by 1,000,000.
What is Dew Point to PPM Conversion?
Dew point to ppm conversion is the process of translating a measured dew point temperature into an approximate water vapor concentration in a gas stream. Since dew point represents the temperature at which water vapor becomes saturated, it can be used to determine the water partial pressure. That partial pressure is then compared with the total pressure of the gas mixture to estimate ppm(v).
This relationship is widely used in engineering, environmental monitoring, laboratory work, compressed gas systems, and industrial drying applications where moisture content may be reported as dew point, partial pressure, or ppm(v).
How to Calculate Dew Point to PPM?
The following steps outline how to convert dew point to ppm(v).
- First, determine the dew point temperature Td in °C.
- Next, determine the total gas pressure ptotal in kPa.
- Calculate the saturation vapor pressure of water at the dew point using the Magnus-type equation.
- Finally, compute PPM(v) ≈ 10⁶ × psat / ptotal.
- After inserting the values and calculating the result, check your answer with the calculator above.
Example Problem:
Use the following values as an example problem to test your knowledge.
Dew Point (Td) = 10 °C
Total Pressure (ptotal) = 101.325 kPa
At 10 °C, the saturation vapor pressure is about 1.228 kPa, so the approximate concentration is:
PPM(v) \approx 10^6 \times \frac{1.228}{101.325} \approx 12{,}000Dew Point to PPM Conversion Table
The table below lists approximate relationships between dew point, saturation vapor pressure, and ppm(v) at 1 atm = 101.325 kPa.
| Dew Point (°C) | Saturation Vapor Pressure (kPa) | Approximate Water Vapor Concentration (ppm) |
|---|---|---|
| -10 | 0.286 | ≈ 2,800 ppm |
| 0 | 0.611 | ≈ 6,000 ppm |
| 10 | 1.228 | ≈ 12,000 ppm |
| 20 | 2.338 | ≈ 23,000 ppm |
| 30 | 4.246 | ≈ 42,000 ppm |
Values are rounded for clarity but follow the same formulas used in the calculator. Increasing total pressure at the same dew point lowers the ppm(v) value because the same water partial pressure is diluted into a higher overall pressure.
Understanding this conversion helps compare moisture readings reported as dew point, relative humidity, or ppm(v), and supports consistent interpretation across different instruments and reference tables.