VFR, MVFR, IFR, LIFR: The Ceiling and Visibility Thresholds

Flight category is the one-word summary of how much the sky and the air are working against you, and it comes from just two numbers: ceiling and visibility. IFR means a ceiling of 500 to below 1,000 feet or visibility of 1 to below 3 statute miles, and wxdecoder.com color-codes each station to that standard, so a glance at the map tells you which fields are open to the eye and which are buried. Learn the four thresholds once and you can read any station's color without looking it up.

This guide covers the four US categories, the exact cutoffs, the rule that the worse of ceiling and visibility wins, and a worked example where visibility alone drives the result. It is part of the METAR field guide, and it leans on two siblings: how to find the ceiling among the cloud layers and how to read METAR visibility.

The four categories

The US uses four flight categories, ordered from best to worst: VFR, MVFR, IFR, and LIFR. Each is defined by a ceiling band, a visibility band, or both. Here are the exact thresholds:

Two things in that table do the heavy lifting. VFR is the only row joined by AND: to be VFR a field needs a ceiling above 3,000 feet and visibility above 5 statute miles. Every worse category is joined by and/or, meaning a single bad number is enough to drop you into it. A 6,000-foot ceiling with 2 SM of visibility is not VFR, and it is not MVFR either, because the visibility alone reaches into the IFR band.

The worst of the two wins

The category is not an average and not a judgment call. The METAR-decoding logic computes a category from the ceiling on its own, computes a category from the visibility on its own, and then reports whichever of the two is worse. There is no trading one off against the other. A brilliant, unlimited-visibility day under a 700-foot overcast is IFR, because the ceiling is IFR no matter how far you can see horizontally.

This is why the categories feel conservative, and that is by design. The number that hurts you most is the one that decides the color, so the worst case is always the one surfaced first.

What counts as a ceiling

The ceiling is not just any cloud. It is the lowest layer reported as broken (BKN), overcast (OVC), or a vertical-visibility group (VV). FEW and SCT layers, by definition 1 to 4 oktas of coverage, are never ceilings, so they do not enter the category math at all. Which layers count, and why FEW and SCT are excluded, is the whole subject of FEW, SCT, BKN, OVC: which layers are a ceiling.

A VV group deserves its own mention. When the sky is so obscured that the observer cannot make out distinct layers, the report gives a vertical visibility instead, for example VV004 for 400 feet. That counts as an indefinite ceiling at that height, and it feeds the category exactly as a BKN or OVC of the same height would. The details are in VV001 and indefinite ceilings.

When there is no ceiling at all, because the sky is clear or carries only FEW and SCT layers, the category comes from visibility alone. A clear sky with 1/2 SM in fog is LIFR on the strength of the visibility, with no ceiling needed to get there.

A worked example where visibility governs

Take this observation:

KXYZ 121651Z 09008KT 2SM BR BKN040 18/16 A2998

Walk the two numbers:

• Ceiling: the lowest BKN/OVC/VV layer is BKN040, a broken layer at 4,000 feet AGL. A 4,000-foot ceiling is greater than 3,000, so on ceiling alone this field is VFR.
• Visibility: 2SM is 2 statute miles. That falls in the 1-to-below-3 band, which is IFR.

The worst of the two wins, so the station is IFR. The roomy 4,000-foot ceiling never gets a vote, because the haze (BR is mist) has pulled visibility down into the IFR range on its own. This is the single most common surprise for new readers: a comfortable-looking ceiling under an IFR or LIFR color, sitting there because the visibility number is the one in trouble.

Flip it around and the same rule holds. Ten miles of visibility under a BKN007 (a 700-foot ceiling) is also IFR, this time on the ceiling. Either number can be the one that decides it.

UNKN: when the category cannot be computed

Sometimes a station shows UNKN rather than a category. That is not a fifth, worst level. It means the category could not be determined, usually because the observation is incomplete (a missing ceiling or visibility field) or because it has expired and there is no current data to score. Treat UNKN as "look closer," not as "the worst kind of weather." Open the raw report and see what is actually missing.

A note on what the color is for

A flight category is a fast situational-awareness cue, not a clearance and not a go decision. It tells you, at a glance, how the ceiling and visibility at a field compare to the standard thresholds. It does not know your aircraft, your ratings, your personal minimums, or the dozen other factors a real plan weighs. Use the color to decide where to look harder, then read the full report and an official briefing before you act on it.

See the category for any station

Every category reduces to the same two-step check: score the ceiling, score the visibility, keep the worse one. VFR needs both numbers to be good; every other category needs only one to be bad. When you want it done for you, paste a raw METAR into wxdecoder and it computes the category, shows the color, and lists the ceiling and visibility it used to get there. To go deeper on the inputs, read how to find the ceiling in the cloud layers and how to decode METAR visibility next.

Last updated June 29, 2026