Aviation Flight Categories
Flight categories — VFR, MVFR, IFR, and LIFR — summarize how good or bad the weather is for flying using just two numbers: the ceiling and the visibility. They are the color-coded labels you see on aviation weather maps. This guide gives the exact thresholds, the rule for combining ceiling and visibility, and how to use categories without over-trusting them.
The two inputs
A flight category is derived from only two values:
- Ceiling — the height of the lowest broken (BKN), overcast (OVC), or vertical-visibility (VV) layer, in feet above ground level. Few and scattered layers do not count. See Cloud & Ceiling Codes.
- Visibility — the prevailing surface visibility in statute miles.
The thresholds
| Category | Ceiling (AGL) | Visibility (SM) |
|---|---|---|
| VFR | Greater than 3,000 ft | Greater than 5 SM |
| MVFR | 1,000 to 3,000 ft | 3 to 5 SM |
| IFR | 500 to below 1,000 ft | 1 to below 3 SM |
| LIFR | Below 500 ft | Below 1 SM |
VFR is Visual Flight Rules; MVFR is Marginal VFR; IFR is Instrument Flight Rules; LIFR is Low IFR. The colors above — green, blue, red, magenta — are the standard shades used on aviation weather charts and match the categories shown in the MetarDecoder output.
The more-restrictive rule
Ceiling and visibility are evaluated separately, and the category is the worse (more restrictive) of the two. You never average them and you never pick the better one.
- Find the category the ceiling alone would give.
- Find the category the visibility alone would give.
- The final category is whichever of those two is more restrictive.
Worked examples
| Ceiling | Visibility | Category | Why |
|---|---|---|---|
| BKN050 (5,000 ft) | 10 SM | VFR | Both are VFR |
| BKN015 (1,500 ft) | 10 SM | MVFR | Ceiling is MVFR, visibility VFR — take MVFR |
| OVC008 (800 ft) | 4 SM | IFR | Ceiling is IFR, visibility MVFR — take IFR |
| OVC020 (2,000 ft) | 1/2 SM | LIFR | Visibility is LIFR, ceiling MVFR — take LIFR |
| No ceiling | 3/4 SM | LIFR | Visibility alone drives it |
The fourth row is the classic trap: a comfortable 2,000-ft ceiling paired with half-mile visibility is still LIFR, because visibility is the limiting factor.
Categories are not legal minimums
Where flight categories appear
You rarely compute a category by hand in practice — it is displayed for you, colour-coded, almost everywhere aviation weather is shown. The NWS Graphical Forecast for Aviation, the station-model maps on aviationweather.gov, and every major electronic flight bag app paint airports green, blue, red, or magenta so you can scan a whole region at a glance and see where the weather is good and where it is not. Knowing the thresholds lets you sanity-check those colours against the raw report.
Why just ceiling and visibility?
Ceiling and visibility are the two conditions that most directly determine whether a pilot can navigate and stay clear of terrain and other aircraft by looking outside. They are measured consistently at nearly every reporting station, which makes them ideal for a standardised, comparable rating. Other hazards matter enormously, but they are harder to reduce to a single number, so they are carried separately in AIRMETs, SIGMETs, and pilot reports rather than folded into the category.
How a TAF forecasts a category
Because a TAF forecasts ceiling and visibility over time, it also implies a forecast flight category for each part of its valid period. A line reading BECMG 1216/1218 2SM OVC008 is forecasting a change into IFR conditions, while FM131500 P6SM SCT050 forecasts a return to VFR. Reading the categories a TAF implies is often more useful than reading the raw numbers, because it tells you directly whether you can expect to fly your intended rules.
A few more worked cases
| Ceiling | Visibility | Category |
|---|---|---|
| BKN012 (1,200 ft) | 6 SM | MVFR |
| OVC009 (900 ft) | 5 SM | IFR |
| No ceiling | 2 SM | IFR |
| OVC004 (400 ft) | 5 SM | LIFR |
Categories are not the regulations
It is worth repeating: VFR, MVFR, IFR, and LIFR are a weather-planning shorthand, not the legal weather minimums you must meet. The actual visibility and cloud-clearance requirements for flight under visual rules depend on the class of airspace, your altitude, and whether it is day or night, and they are set out in the regulations — in the United States, 14 CFR 91.155. An airport labelled "VFR" on a map can still sit in airspace where a specific operation is not legal without meeting those separate minimums.
Personal minimums
Many pilots set personal minimums more conservative than both the categories and the regulations — for example, treating anything below a 3,000-ft ceiling or 8 miles of visibility as a no-go early in their flying. The category system is a useful anchor for building those limits, because it gives you a consistent vocabulary for "how bad is it" that matches the tools you already use.
Common mistakes
- Averaging ceiling and visibility. Each is judged separately and the worse one wins.
- Picking the better of the two values instead of the more restrictive one.
- Assuming a good category means safe conditions — icing, turbulence, and storms are not captured.
- Treating the category as legal permission to fly VFR without checking the actual minimums.
Limitations
A category collapses a complex sky into one label. It does not account for icing, turbulence, thunderstorms, mountain obscuration, or how fast conditions are changing. An airport can read VFR while an embedded thunderstorm sits five miles away. Use the category as a first glance, then read the full METAR and TAF, plus AIRMETs, SIGMETs, and pilot reports, before you decide.
Always verify officially
Official sources
- FAA Aviation Weather Handbook (FAA-H-8083-28); Aeronautical Information Manual (AIM).
- NWS Aviation Weather Center — aviationweather.gov (flight-category definitions used on the GFA and METAR maps).