METAR Visibility: From 1/4SM to P6SM Explained

Visibility is the group that, alongside the ceiling, decides how much you can legally and comfortably see, and it sits right after the wind in a METAR. In a US report it is written in statute miles with an SM suffix: 10SM, 3SM, or a fraction like 1/2SM. P6SM means visibility greater than 6 statute miles, the highest value a US METAR reports, while 1/4SM is the lowest standard increment. Paste a raw report into wxdecoder and the visibility group is pulled out and labeled in plain language. This guide covers the US statute-mile format, the ICAO meters format, and how the number sets your flight category.

It is part of the METAR field guide. For the runway-specific value that often appears alongside it in low visibility, see runway visual range.

US statute miles: the SM suffix

A US METAR reports prevailing visibility in statute miles followed by SM. Prevailing means the greatest distance you can see over at least half the horizon circle, so it is a single representative number for the whole field rather than a per-direction reading.

Whole and partial miles look like this:

10SM     ten statute miles
3SM      three statute miles
1 1/2SM  one and one-half statute miles

When visibility drops below one mile, the report switches to a plain fraction:

3/4SM    three-quarters of a mile
1/2SM    one-half mile
1/4SM    one-quarter mile

1/4SM is the lowest standard increment you will normally see. Note the space in 1 1/2SM: the whole number and the fraction are separated, which is why a value just above a mile reads as two pieces rather than one run-together token.

P6SM: the "greater than 6" ceiling on the number

US visibility is capped at the top end. Once the prevailing visibility is better than 6 statute miles, the report stops counting and writes P6SM. The P stands for "plus," meaning greater than. So a hazy day with exactly 7 miles and a crystal-clear day with unlimited visibility both read P6SM.

That cap is deliberate. For flight-category and operational purposes, anything past 6 miles is functionally "good," so there is no need to distinguish 8 miles from 40. When you see P6SM, read it as "visibility is not the limiting factor," and look to the ceiling for the rest of the picture.

ICAO meters: 5000, 9999, and padding

Outside the US, METARs that follow the core ICAO format report visibility in meters with no unit suffix. The number is just meters:

5000     5000 meters (5 km)
2000     2000 meters
0800     800 meters

Two conventions are worth memorizing. First, values below 1000 meters are padded to four digits, so 800 meters is written 0800, not 800. Second, 9999 is a special code: it means visibility of 10 km or more. It is the meters-format equivalent of the US P6SM, the "everything past this point is good" value. A bare 0000 at the other extreme indicates visibility below 50 meters.

Because the two systems look nothing alike, the unit tells you which one you are reading: a trailing SM is statute miles, a bare four-digit number is meters.

How visibility sets the flight category

Visibility is one of the two inputs to the US flight category, the other being the ceiling. The category is the worse of what the visibility allows and what the ceiling allows, so a great ceiling cannot rescue a poor visibility, and the other way around. The visibility-only thresholds are:

If there is no ceiling at all, the category comes from visibility alone. The full rule, including how the ceiling thresholds interact with these, is in VFR, MVFR, IFR, LIFR. The short version: the worst of ceiling and visibility wins, so always read both groups together before you judge a field.

A side-by-side example table

The same conditions look different depending on which format a station uses. Reading them next to each other builds the habit of converting on sight:

The meters values above are approximate, since the two systems round to different increments, but they show how a single drop in visibility moves a field down through the categories. A worked report puts the group in context:

KSFO 211956Z 28012KT 1/2SM FG VV002 14/13 A2998

Here 1/2SM is half-mile visibility, the FG is fog explaining why, and the VV002 is an indefinite ceiling at 200 feet. Visibility alone (below 1 mile) already forces LIFR; see vertical visibility for what the VV group adds. You can confirm any of this by dropping the report into the decoder, which separates the visibility, weather, and ceiling so you are not parsing the string in your head.

Decode any visibility group instantly

The rule set is small: US reports use statute miles with SM, fractions below one mile down to 1/4SM, and P6SM for anything better than 6 miles; ICAO reports use meters, padded below 1000, with 9999 for 10 km or more. Whichever you are reading, the number feeds the flight category alongside the ceiling. When you want it read for you, paste the raw report into wxdecoder and the visibility group is translated into a labeled line. To see how it combines with the ceiling, read the flight categories next.

Last updated June 29, 2026