What is the Wi-Fi MCS index?

The Modulation and Coding Scheme (MCS) index is a number that describes which modulation (BPSK to 4096-QAM) and which coding rate (1/2 to 5/6) a Wi-Fi radio uses. Together with the channel width, the number of spatial streams and the guard interval, it sets the PHY data rate. 802.11n uses MCS 0–7 per stream, 802.11ac 0–9, 802.11ax 0–11 and 802.11be 0–13.

How is a Wi-Fi data rate calculated from the MCS index?

Data rate = data subcarriers × coded bits per subcarrier × coding rate × spatial streams ÷ symbol duration (OFDM symbol plus guard interval). For example, 802.11ax at 80 MHz with 2 spatial streams, MCS 11 and a 0.8 µs guard interval gives 980 × 10 × 5/6 × 2 ÷ 13.6 µs = 1201.0 Mb/s.

What is the maximum Wi-Fi 7 (802.11be) data rate?

With 8 spatial streams, a 320 MHz channel, MCS 13 (4096-QAM 5/6) and a 0.8 µs guard interval, 802.11be reaches 23,058.8 Mb/s. A single stream at 320 MHz reaches 2,882.4 Mb/s, and 2 streams at 160 MHz reach 2,882.4 Mb/s as well.

Why is MCS 9 not available at 20 MHz in 802.11ac?

802.11ac only allows an MCS when the coded bits of one symbol split evenly across its BCC encoders and the puncturing pattern. At 20 MHz, MCS 9 (256-QAM 5/6) only works with 3 or 6 spatial streams; the standard marks the other stream counts as not valid, and this table omits them.

Tools

Wi-Fi MCS Index

PHY data rates · 802.11n / ac / ax / be

28 rows · 39 rate columns

802.11n · Wi-Fi 4

802.11ac · Wi-Fi 5

802.11ax · Wi-Fi 6 / 6E

802.11be · Wi-Fi 7

20 MHz

40 MHz

20 MHz

40 MHz

80 MHz

160 MHz

20 MHz · 242-tone RU

40 MHz · 484-tone RU

80 MHz · 996-tone RU

160 MHz · 2×996-tone RU

20 MHz · 242-tone RU

40 MHz · 484-tone RU

80 MHz · 996-tone RU

160 MHz · 2×996-tone RU

320 MHz · 4×996-tone RU

MCS

Modulation

Coding

800 ns

400 ns

800 ns

400 ns

800 ns

400 ns

800 ns

400 ns

800 ns

400 ns

800 ns

400 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

3.2 µs

1.6 µs

800 ns

1 spatial stream

BPSK

1/2

QPSK

1/2

QPSK

3/4

16-QAM

1/2

16-QAM

3/4

64-QAM

2/3

64-QAM

3/4

64-QAM

5/6

256-QAM

3/4

—

256-QAM

5/6

—

1024-QAM

3/4

—

1024-QAM

5/6

—

4096-QAM

3/4

—

4096-QAM

5/6

—

2 spatial streams

BPSK

1/2

QPSK

1/2

QPSK

3/4

16-QAM

1/2

16-QAM

3/4

64-QAM

2/3

64-QAM

3/4

64-QAM

5/6

256-QAM

3/4

—

256-QAM

5/6

—

1024-QAM

3/4

—

1024-QAM

5/6

—

4096-QAM

3/4

—

4096-QAM

5/6

—