How to say numbers on the radio: altitudes, headings, frequencies and squawks

Why numbers get their own rules

Most of what you say on the radio is numbers: altitudes, headings, frequencies, altimeter settings, squawk codes, runways, times. They are also where most mishearings happen. "Two" and "ten" or "five" and "nine" sound alike through a noisy headset, so aviation fixes both how each digit sounds and how numbers are grouped.

In the US the pilot side is in the FAA Aeronautical Information Manual (AIM 4-2-7 to 4-2-12), and the controller side is in FAA Order JO 7110.65, paragraph 2-4-17 (Numbers Usage). Outside the US you follow ICAO-based rules; in Europe that means SERA, and the UK CAA's CAP 413 radiotelephony manual is a free, readable reference built on it. The basics are the same everywhere, but a few details change, and those details are worth knowing if you fly or train on both sides.

How each digit sounds

AIM 4-2-7 lists a pronunciation for every digit. The point is not an accent. Each word is picked so it can't be confused with another one.

CAP 413 uses the same set and adds the words for decimal (DAY-SEE-MAL), hundred and thousand (TOUSAND).

Tip: "niner" and "fife" feel strange at first. Use them from your first lesson anyway. It is much harder to fix the habit later than to build it now.

The default: say every digit

Both the FAA and ICAO start from the same rule: unless there is a specific exception, pronounce each digit separately. AIM 4-2-8 puts it as "all other numbers must be transmitted by pronouncing each digit," with 10 spoken as "one zero". JO 7110.65 2-4-17 applies it to headings, wind, altimeter settings, beacon codes, runways and frequencies.

So you never say "heading two-seventy" or "squawk twelve hundred" in a by-the-book transmission. You say the digits.

Altitudes: the main exception

Altitudes are where "hundred" and "thousand" come in.

FAA (AIM 4-2-8 and 4-2-9):

• Round hundreds and thousands up to 9,900: "five hundred", "four thousand five hundred"
• Above 9,900, say the digits before "thousand": 10,000 is "one zero thousand", 13,500 is "one three thousand five hundred"
• Below 18,000 feet MSL, the same pattern: 12,500 is "one two thousand five hundred"
• At and above 18,000 feet (FL180), say "flight level" plus the digits: FL190 is "flight level one niner zero"

JO 7110.65 adds that controllers may restate an altitude in group form ("ten thousand") for clarity, after saying it the standard way.

ICAO / UK (CAP 413, Chapter 2): whole hundreds and thousands work the same way for altitude, height, cloud height and visibility: 2,500 is "two thousand five hundred". Flight levels are digit by digit, but CAP 413 makes FL100, FL200 and FL300 "flight level one hundred / two hundred / three hundred" to avoid confusing 100 with 110 or 200 with 220. It also says "hundred" must never be used for headings.

Headings, courses and wind

AIM 4-2-10: bearings, courses, headings and wind directions are three digits and magnetic. Add "true" only when it is true.

• Heading 100 is "heading one zero zero"
• Course 005 is "zero zero five"
• Wind 220 is "wind two two zero"

JO 7110.65 says controllers omit the word "degrees" on headings and use 360, not 000, for north. Surface wind is "wind" plus the direction, "at", and the speed: "wind two seven zero at one five gusts three five". In UK practice (CAP 413, Chapter 3), "degrees" is added to headings that end in zero, or wherever confusion could arise.

Frequencies: "point" vs "decimal"

This is the difference you'll notice first if you move between the US and Europe.

• FAA: digits plus "point": 122.1 is "one two two point one" (AIM 4-2-8). JO 7110.65 also says to drop digits after the second one past the decimal point.
• ICAO: the decimal point is spoken as "decimal". AIM 4-2-8 notes this and says the FAA will honor it from aircraft that use ICAO procedures.
• UK / 8.33 kHz airspace: CAP 413 says to use all six figures, whether the frequency is 25 kHz or 8.33 kHz spaced, except when the last two digits are both zero. 118.125 is "one one eight decimal one two five", while 118.000 is just "one one eight decimal zero".

The frequency is something you always read back. The readback guide covers what else belongs on that list.

Altimeter settings and squawk codes

Altimeter (FAA): JO 7110.65: "altimeter" followed by the separate digits, so 30.01 is "altimeter three zero zero one". A controller may add the group form for clarity: "altimeter two niner niner two, twenty-nine ninety-two".

QNH (ICAO / UK): pressure settings in hectopascals are digit by digit, but a whole thousand uses the word: CAP 413 gives QNH 1000 as "one thousand". It also adds the word "hectopascals" whenever the setting is below 1000 hPa, so nobody reads 998 as 29.98.

Squawk codes: this is a genuine FAA vs UK difference.

• JO 7110.65: beacon codes are four separate digits. 1000 is "one zero zero zero", 2100 is "two one zero zero".
• CAP 413: codes are digit by digit (6500 is "six five zero zero"), but whole thousands use "thousand": squawk 1000 is "one thousand". CAP 413 points to SERA.14035 for this.

The US VFR code is 1200 (AIM 4-1-20), and you'll hear "squawk VFR" for it. CAP 413 calls 7000 a conspicuity code in the UK. Other countries publish theirs in their own AIP, so check before you fly there.

Runways, speeds and time

• Runways (JO 7110.65): "runway" plus the separate digits, adding left, right or center. 27R is "runway two seven right", 3 is "runway three".
• Speeds (AIM 4-2-11): separate digits plus "knots": 190 is "one niner zero knots".
• Traffic positions: clock positions are the one place digits are said together. CAP 413, citing SERA.14035, gives "ten o'clock" and "eleven o'clock", and JO 7110.65 has "traffic, one o'clock, two five miles".
• Time (AIM 4-2-12): aviation uses UTC, which you can call "Zulu". 0920 UTC is "zero niner two zero". If you give local time, you must say "local". When no confusion is likely, minutes only are fine: at 14:20, "two zero".

Common student mistakes

1. "Oh" instead of "zero" in headings and squawks ("heading two seven oh")
2. Group form by habit: "squawk twelve hundred", "heading two-seventy"
3. Dropping "thousand" on altitudes: "climb four five" is not "four thousand five hundred"
4. Changing the order of numbers in a readback, which makes the controller doubt you got them right
5. "Point" vs "decimal" panic when switching regions. Either one will be understood. What matters is the digits.

Tip: if you're not sure you heard a number right, don't guess. Say "say again" or read back what you think you heard so the controller can correct it.

FAA vs ICAO at a glance

How to practice

• Read numbers aloud from a real chart, a METAR or an ATIS: frequencies, field elevation, runway, altimeter
• Have a friend read you random four-digit squawks and altitudes and answer in correct form, out loud, without pausing
• Read back full clearances, keeping the numbers in the order you heard them

If you want a controller that talks back and checks your numbers, you can practice with KoAir in English or Spanish.

Related: the ICAO phonetic alphabet and ATC clearance readbacks.