Wi-Fi Frame Airtime Calculator
How long does one Wi-Fi transmission really take? Pick a frame and how it is sent, and see every microsecond: waiting for the channel, the preamble, the data symbols, padding, SIFS and the acknowledgement, calculated with the TXTIME formulas of IEEE 802.11.
Why airtime matters
Only one device can send on a channel at a time, so what limits a Wi-Fi network is time, not bits. Every transmission pays a fixed cost before its data (the wait for the channel and the preamble) and after it (padding, a short gap and the acknowledgement). For a big frame at a high rate that cost is small; for a small frame, or anything sent at a legacy rate, it can be most of the time. This calculator shows exactly how much, for 802.11b through Wi-Fi 7.
3 · Where the time goes
Waiting (AIFS + backoff)RTS/CTSLegacy preamble (L-STF, L-LTF, L-SIG)HT/VHT/HE/EHT preambleData symbolsPacket extension and signal extensionSIFSAck or Block Ack
4 · Step by step
The TXTIME calculation from the standard, with the numbers above. With two settings, the first one is shown.
Definitions
↗ opens a term's full entry in the Wi-Fi Glossary, which explains over 400 Wi-Fi terms with their IEEE 802.11 references.
Notes
- Exact where the standard is exact. The PPDU durations follow the TXTIME equations of the standard: DSSS IEEE 802.11-2024 15.4.6.7, HR/DSSS IEEE 802.11-2024 16.3.4, OFDM IEEE 802.11-2024 17.4.3, ERP IEEE 802.11-2024 18.5.3.2, HT IEEE 802.11-2024 19.4.3, VHT IEEE 802.11-2024 21.4.3, HE IEEE 802.11-2024 27.4.3 and EHT IEEE 802.11be-2024 36.4.3. That includes the HE and EHT pre-FEC padding, the LDPC extra symbol segment (IEEE 802.11-2024 19.3.11.7.5) and packet extension (IEEE 802.11-2024 27.3.13, IEEE 802.11be-2024 36.3.14).
- Assumptions: single-user transmissions on the whole channel (no OFDMA or MU-MIMO), no STBC, HT mixed format, LDPC coding for VHT, HE and EHT (BCC or LDPC for HT), the packet extension equal to its nominal value, EHT-SIG sent at EHT-SIG-MCS 0, no midambles. The waiting time uses the default EDCA parameters (IEEE 802.11-2024 Table 9-194), a 9 µs slot (20 µs for 802.11b; in 2.4 GHz that assumes no 802.11b devices in the BSS, so the short slot is used) and the average backoff, CWmin ÷ 2 slots, as if the channel were idle; on a busy channel the wait is longer.
- Frame sizes: a data frame is a QoS Data MPDU: 26-byte MAC header, 8-byte LLC/SNAP header, the payload, the encryption header and MIC, and a 4-byte FCS. In an A-MPDU each frame adds a 4-byte delimiter and is padded to a multiple of 4 bytes. VHT, HE and EHT always send data in an A-MPDU, even a single frame. Control frames: Ack and CTS 14 bytes, RTS 20 bytes, compressed Block Ack 32 bytes with a 64-frame bitmap, 56 bytes for 256 frames (IEEE 802.11-2024 Table 9-38), and 88 or 152 bytes for 512 or 1,024 frames in EHT. The tool warns when a frame is larger than the limits in IEEE 802.11-2024 Table 9-34 (a 2,304-byte MSDU without A-MSDU, a 7,935-byte A-MSDU for HT, an 11,454-byte MPDU for VHT, HE and EHT).
- Control frames and beacons are sent in a non-HT PPDU at a basic rate: the rate you choose in "Basic rate for Acks, RTS/CTS and beacons".