Wi-Fi Frame Airtime Calculator
How long one Wi-Fi frame really takes, from 802.11b to Wi-Fi 7: the wait for the channel, the preamble, the data symbols, padding and the Ack, with the TXTIME calculation drawn step by step.
How to use this tool controls and what to look for
Choose a frame and how it is sent, and see how long it takes on the air, split into the wait, preamble, data, padding and Ack.
Controls to change
- Frame: choose Data, Beacon, Ack, Block Ack, RTS or CTS.
- Payload per frame (bytes, for example an IP packet): set the payload size. Frames sent together (A-MPDU) aggregates several.
- Encryption: add CCMP-128 or GCMP-256 overhead.
- Access category: change the wait for the channel (Best effort, Background, Video, Voice).
- Protect with RTS/CTS first: add an RTS/CTS exchange in front.
- Compare two settings: set up two versions side by side, for example two rates or two generations.
What to look for
- A small frame at a high rate is mostly overhead: the preamble and the wait for the channel can take longer than the data.
- Legacy rates stretch every frame. The same payload at 1 Mbps takes many times longer than at 54 Mbps.
- Aggregating frames into one A-MPDU pays the overhead once, so the effective throughput rises sharply.
- The step-by-step section shows how bits fill OFDM symbols and where the padding comes from.
About this tool
Pick a frame (data, beacon, Ack, Block Ack, RTS or CTS) and how it is sent, from 802.11b to Wi-Fi 7, and this calculator shows every microsecond of the exchange: waiting for the channel, the preamble fields, the data symbols, padding and packet extension, SIFS and the acknowledgement. The PPDU durations follow the TXTIME equations of IEEE 802.11-2024 and 802.11be-2024, including HE and EHT pre-FEC padding and the LDPC extra symbol, and a step-by-step card draws how each number is worked out. Compare two settings side by side to see what a wider channel, a higher MCS or aggregation really saves.
What you'll learn
- Why airtime, not bits, limits a Wi-Fi network, and why small frames and legacy rates waste so much of it
- What each part of a PPDU costs: the legacy preamble, the HT/VHT/HE/EHT preamble, the data symbols and the packet extension
- How bits fill OFDM symbols, and where padding, the LDPC extra symbol and the pre-FEC padding factor come from
- How much A-MPDU aggregation, RTS/CTS and the Ack or Block Ack change the time for one exchange
Common questions
How long does a 1500-byte frame take on Wi-Fi 6?
At HE MCS 9, 80 MHz and two spatial streams the PPDU itself lasts about 82 µs, but with the wait for the channel, SIFS and the Ack the whole exchange takes about 236 µs, so the data symbols are only around 12% of the time.
Why does aggregation make Wi-Fi so much faster?
The fixed costs (the wait for the channel, the preamble, SIFS and the acknowledgement) are paid once per PPDU. Sending many frames in one A-MPDU spreads that cost over all of them, so the share of time spent carrying data goes up.
What is the packet extension?
Extra time after the last data symbol of an HE or EHT PPDU that gives the receiver time to finish decoding. Its length depends on how full the last symbol is and on the padding the receiver asked for, from 0 to 16 µs in HE and up to 20 µs in EHT.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.