Numbers & Metrics

p99 — "pee ninety-nine" or "percentile ninety-nine":

The "p" in p99 stands for "percentile". In speech:

• "pee ninety-nine" — the most common casual form in engineering teams. "99" is read as "ninety-nine", not as two separate digits.
• "percentile ninety-nine" — the explicit form used in presentations or with non-technical audiences.

NOT correct: "pee nine-nine" — reading each digit separately is unusual for percentile notation.

Related percentile pronunciations:

• p50 — "pee fifty" (median)
• p95 — "pee ninety-five"
• p99.9 — "pee ninety-nine point nine"

Full formula in a sentence: "Our SEE-ELL-AY requires p99 latency below 200 milliseconds" = "Our SLA requires percentile ninety-nine latency below 200 milliseconds."

KB vs KiB — two distinct spoken units:

The IEC 80000-13 standard introduced binary prefixes to disambiguate:

• KB (kilobyte) = 1,000 bytes — SI decimal prefix. Read: "KAY-BEE" or "kilobyte".
• KiB (kibibyte) = 1,024 bytes = 2¹⁰ bytes. Read: "KIB" (/kɪb/) or "kibibyte" ("KIB-ee-byte").

In practice: Many engineers still say "kilobyte" for 1,024 (the old convention), which creates ambiguity. In precise contexts (kernel docs, storage hardware, SLA contracts), use KiB/MiB/GiB.

Full binary prefix table:

• KiB — "KIB" / "kibibyte" — 2¹⁰
• MiB — "MIB" / "mebibyte" — 2²⁰
• GiB — "GIB" / "gibibyte" — 2³⁰
• TiB — "TIB" / "tebibyte" — 2⁴⁰

Scientific notation in speech — convert to named units:

3.14×10⁻³ s = 0.00314 s = 3.14 milliseconds.

In verbal communication, always convert to a named unit when one exists — listeners can process "3.14 milliseconds" instantly, but "three point one four times ten to the minus three" requires mental arithmetic.

Correct reading if you must use scientific notation: "three point one four times ten to the power of negative three seconds" (option A). "e minus three" (option B) is shorthand from programming notation (3.14e-3) — acceptable informally but not in presentations.

Common time conversions for benchmarks:

• 1×10⁻³ s = 1 ms (millisecond) — "one millisecond"
• 1×10⁻⁶ s = 1 µs (microsecond) — "one microsecond"
• 1×10⁻⁹ s = 1 ns (nanosecond) — "one nanosecond"

Saying µs (microsecond): /ˈmaɪkroʊˌsɛkənd/ — "MY-kro-sek-und" — never "mew-second".

Version numbers — two dominant patterns:

Version numbers follow one of two conventions in speech:

Pattern 1 — read segments as numbers: "version three eleven two" — treats each segment (3, 11, 2) as a number without "point". Common in fast developer conversation: "we shipped three eleven two", "running three eleven".

Pattern 2 — use "point": "version three point eleven point two" — the dots between segments are spoken as "point". Common in documentation readings and more formal presentations.

NOT standard: "three point one one point two" — reading each digit individually is unusual for standard SemVer. It's only used when digit confusion is likely (e.g., v1.10 vs v1.1 — then "one ten" vs "one one" may be disambiguated as "one-one-zero" vs "one-one").

Semantic versioning spoken:

• MAJOR.MINOR.PATCH → "major eleven, minor two" is never used — just read the numbers
• "release candidate" → v3.0.0-rc.1 = "version three zero zero release candidate one"

99.99% uptime — "four nines" — ~52 minutes/year:

Two accepted ways to say it:

• "ninety-nine point nine nine percent uptime" — reading the number verbatim
• "four nines uptime" — the shorthand used in SRE, SLA, and DevOps conversations

"Four nines" counts the nines in the percentage: 99.99% → four 9s → "four nines".

Uptime table — essential for SRE conversations:

• 99% — "two nines" — ~3.65 days/year downtime
• 99.9% — "three nines" — ~8.76 hours/year
• 99.99% — "four nines" — ~52.6 minutes/year
• 99.999% — "five nines" — ~5.26 minutes/year

In a sentence: "Our SLA guarantees four nines — that's about 52 minutes of allowed downtime annually."

Option C is wrong — 8.7 hours/year is three nines (99.9%), not four.