Enter measurement details
MG/L and g/m³ have the same numerical value for water vapor concentration.
Formula used
The calculator first estimates saturated vapor pressure from air temperature. It then calculates saturated absolute humidity and compares your measured moisture concentration against it.
Saturation vapor pressure: eₛ = 6.112 × exp[(17.62 × T) ÷ (243.12 + T)]
Saturation absolute humidity: AHₛ = 216.7 × eₛ ÷ (T + 273.15)
Relative humidity: RH = (AH ÷ AHₛ) × 100
T is temperature in Celsius. Vapor pressure values use hPa. Absolute humidity values use g/m³. MG/L equals g/m³ numerically.
How to use this calculator
- Measure or enter water vapor concentration in mg/L.
- Select the moisture unit that matches your instrument.
- Enter air temperature and choose its unit.
- Select the decimal precision you need.
- Press Calculate Humidity to view the percentage and details.
- Use Download CSV or Print or Save PDF for records.
Example data
| Moisture | Temperature | Estimated RH | Meaning |
|---|---|---|---|
| 5 mg/L | 22 °C | About 26% | Dry air |
| 10 mg/L | 22 °C | About 52% | Common comfort range |
| 15 mg/L | 22 °C | About 78% | Humid air |
Understanding MG/L and relative humidity
Understanding Moisture Concentration
Air can hold water vapor without appearing wet. Absolute humidity describes the water amount in a volume of air. This calculator accepts milligrams per liter. That unit is numerically equal to grams per cubic meter. Relative humidity is different. It compares the present water vapor with the maximum possible amount at the same temperature. Temperature therefore changes the result.
Why Temperature Changes the Percentage
Warm air can contain much more vapor than cool air. A reading of 10 mg/L may feel dry at a high temperature. The same reading may indicate very damp air at a low temperature. The calculator estimates the saturation limit from the entered air temperature. It then divides your actual moisture value by that limit. The percentage shows how close the air is to saturation.
Interpreting the Result
A relative humidity value between 30% and 60% is often comfortable indoors. Lower values may increase dry skin, throat irritation, static electricity, and wood shrinkage. Higher values can encourage condensation, dust mites, and mold growth. Context still matters. Ventilation, surface temperature, outdoor weather, and occupancy can change indoor conditions. Use the calculated percentage as a measurement, not a complete building diagnosis.
Useful Extra Readings
The result panel provides saturation vapor pressure, actual vapor pressure, dew point, and vapor pressure deficit. Dew point is the temperature where condensation begins. It helps identify moisture risks near cool windows or walls. Vapor pressure deficit shows the gap between current and saturated moisture pressure. A smaller gap means the air is closer to saturation. These extra readings make the calculator useful for homes, greenhouses, storage rooms, and environmental monitoring.
Working With Different Units
Milligrams per liter and grams per cubic meter have identical numerical values. This is because one cubic meter contains one thousand liters, while one gram contains one thousand milligrams. The calculator also accepts grams per cubic foot. It converts that value before calculating humidity. Select the correct unit first. Incorrect units can produce a large error and may incorrectly suggest saturation.
Limits and Good Measurement Practice
This estimate uses a saturation vapor pressure equation. It is reliable for normal indoor and outdoor temperatures. Sensor placement remains important. Keep humidity sensors away from direct sunlight, heaters, cooling coils, steam outlets, and wet surfaces. Allow the sensor to stabilize before recording a value. Very high calculated percentages may indicate condensation, fog, sensor drift, or an unsuitable input. Compare readings over time for clearer decisions.
Comparing Spaces and Times
Use one consistent measurement time when comparing spaces. Morning readings often differ from afternoon readings because temperature changes. A basement may show a higher percentage even when it contains less total vapor. Record temperature beside every moisture value. For plant care, material storage, or HVAC checks, follow the acceptable range for that specific purpose. This improves trends, comparisons, and action planning efficiently today.
Frequently asked questions
1. Can MG/L convert directly to relative humidity?
No. Relative humidity also depends on air temperature. The same moisture concentration produces different percentages at different temperatures. Enter both values for a meaningful result.
2. Is 1 mg/L equal to 1 g/m³?
Yes. They have the same numerical value for concentration. One cubic meter contains one thousand liters. One gram contains one thousand milligrams.
3. What relative humidity is usually comfortable indoors?
Many indoor spaces target roughly 30% to 60% relative humidity. Personal comfort and building needs vary. Museums, plant rooms, and storage areas may use different limits.
4. Why can the result exceed 100%?
A value above 100% means the entered concentration exceeds the modeled saturation amount. This can suggest condensation, fog, a temperature mismatch, sensor error, or an incorrect unit.
5. Does air pressure affect this calculation?
This tool uses a standard temperature-based vapor pressure method. For normal indoor monitoring, the result is practical. Specialized high-altitude or process applications may need pressure-corrected psychrometric methods.
6. What is dew point?
Dew point is the temperature where air reaches saturation and condensation can begin. A dew point near a cold surface temperature increases the risk of water formation.
7. What is vapor pressure deficit?
Vapor pressure deficit is the difference between saturation vapor pressure and actual vapor pressure. It helps describe drying potential. Lower values mean the air is closer to saturation.
8. Can I use Fahrenheit or Kelvin?
Yes. Select Fahrenheit or Kelvin before calculating. The calculator converts your value to Celsius internally because the saturation equation uses Celsius.
9. How accurate is the result?
Accuracy depends mainly on your sensor and inputs. The equation is suitable for ordinary air temperatures. Use calibrated instruments and stable sampling conditions for stronger results.
10. Can this help with mold prevention?
It can support moisture monitoring. Persistent high humidity and cool surfaces raise condensation and mold risks. Inspect ventilation, leaks, insulation, and surface temperatures alongside this result.
11. Can I save the calculation?
Yes. Use Download CSV to save the numeric readings. Use Print or Save PDF to create a printable record from your browser.