Visibility Calculator
Estimate atmospheric visibility from humidity, precipitation rate, and particulate concentration. Provides aviation flight category and driving safety guidance.
About this calculator
This calculator estimates visibility from three independent empirical curves -- humidity, precipitation, and particulate concentration -- then reports the worst (most restrictive) of the three as the combined Visibility, since fog, rain, and smoke each reduce how far you can see largely independently of one another and the most severe factor typically dominates what a person actually observes. Relative Humidity reduces visibility smoothly across the whole range rather than switching on at a threshold: it is negligible in dry air, becomes the binding factor as haze and mist form above roughly 80%, and falls into fog (under 1 km) near saturation. Precipitation Rate uses a single empirical intensity-to-visibility curve applied to whatever precipitation rate you enter; it does not distinguish rain from snow or other precipitation types, so treat the rate as a general precipitation-intensity input rather than a phase-specific one.
Particulate (PM2.5) reduces visibility as smoke, haze, or dust concentration rises. Primary Limiting Factor reports whichever of the three curves produced the lowest (most restrictive) estimate, which is the one actually controlling the combined Visibility figure.
Inputs
Results
Visibility
11.95 km
≈ 36 Eiffel Towers
Aviation Category
VFR
How to Use This Calculator
- Enter relative humidity (%) — visibility falls smoothly as humidity rises, with the sharpest drop only very close to saturation.
- Set precipitation intensity (mm/hr) — this uses one general rate-based curve, not a rain/snow-specific one.
- Enter PM2.5 particulate concentration (µg/m³) for smoke, haze, or dust effects.
- Review Visibility (km), Visibility (miles), and Visibility (meters) for your conditions.
- Use Aviation Category (VFR/MVFR/IFR/LIFR), Driving Safety rating, and Primary Limiting Factor for activity planning — the aviation category here reflects visibility only; the real category is set by whichever of ceiling or visibility is more restrictive.
How the result changes with Relative Humidity
| Relative Humidity | Visibility | Aviation Category |
|---|---|---|
| 43 | 11.95 km | VFR |
| 64 | 11.95 km | VFR |
| 100 | 0.08 km | LIFR (Low IFR) |
What each input means
- Relative Humidity
- Relative humidity as a percentage. Visibility falls into mist below about 10 km near 93% and into fog (under 1 km) above about 98%.
- Precipitation Rate
- Rainfall intensity in millimeters per hour. Light rain is 0.5-2, moderate 2-7, heavy >7 mm/hr.
- Particulate (PM2.5)
- Fine particulate matter concentration. Good air: <12, moderate: 12-35, unhealthy: 35-150, hazardous: >250 μg/m³.
How this is calculated
Worked example, using the default values
- Identify Input ParametersRelative Humidity = 85, Precipitation Rate = 2, Particulate (PM2.5) = 25 = 3 input(s) provided
- Calculate VisibilityVisibility11.95 = 11.95
- Calculate Aviation CategoryAviation CategoryVFR = VFR
- Calculate VisibilityVisibility7.43 = 7.43
- Calculate VisibilityVisibility11950 = 11950
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does Visibility use the worst of the three factors instead of combining them?
Fog, rain, and smoke each reduce visibility largely independently, and in most real conditions the most severe factor is what actually limits how far you can see -- heavy fog isn't made meaningfully worse by moderate haze layered on top of it. Taking the minimum (most restrictive) of the three empirical estimates approximates that real-world behavior better than averaging or adding them together would.
Does this calculator distinguish rain from snow?
No -- Precipitation Rate uses a single empirical intensity-to-visibility curve regardless of precipitation type. Enter the general precipitation intensity you're modeling; the result does not separately account for whether it's rain, snow, or freezing rain.
At what humidity does visibility actually start dropping?
There's no single threshold -- Relative Humidity reduces visibility smoothly across the whole 0-100% range. The effect is negligible in dry air, becomes noticeable as haze and mist form somewhere above roughly 80%, and falls into fog (under 1 km) only very close to saturation, near 98-99% RH.
What does Primary Limiting Factor tell me?
It names whichever of the three inputs -- humidity/fog, precipitation, or particulate -- produced the lowest (most restrictive) visibility estimate, since that is the factor actually setting the combined Visibility figure. If you want to improve visibility in the modeled scenario, that's the condition that would need to change.
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