Wi-Fi Airtime Calculator
Calculate channel utilization and find how many access points your client load needs.
Start in Beginner mode unless you already know the PHY rates and stream counts you want to model. You can switch to Advanced at any point, and everything you have entered is carried over.
- Choose Beginner for a guided setup, or Advanced to enter PHY rates, spatial streams and per-client demand directly.
- Set the band, channel width and typical signal quality for the AP you are sizing. These apply to every device row.
- Add one row per type of device on the AP. Click + Add device type for each additional group, and Remove to drop a row.
- In each row, pick the device type and how many there are, then what they're doing, unless the device has one fixed job. IP cameras, IoT / sensors, VoIP handsets and video conferencing units have a fixed activity that is set for you. For every other device type, the Mbps value is shown in each activity label; if you pick Custom…, type the demand in Mbps.
- Pick the Wi-Fi standard each row uses. The tool calculates only once every row has a standard selected.
- Click Calculate. The results panel shows how many APs the load needs, the total airtime demand, and which group is consuming more than its share of the channel.
- Use Clear All to empty every field and start over.
Inputs
Radio settings (entered once, above the device rows)
Signal quality sets the assumed MCS index used to derive PHY rates. Better signal means a higher modulation rate, so each megabit of traffic costs less airtime.
Device groups
Results
Fill in every device row and click Calculate, and results appear here.
Cost = airtime share ÷ traffic share. Above 1.0, a group takes more of the channel than its traffic contributes. This is the number that identifies what to fix.
| Group | Clients | PHY rate | Traffic | Traffic share | Airtime | Cost |
|---|
Why time is the shared resource
Only one device can transmit on a channel at a moment in time, so what an access point divides between its clients is time, not megabits. A client's airtime is its traffic divided by its PHY rate, so a slow client needs far more of the channel to move the same data. A device talking at 6 Mbps occupies more than a hundred times the airtime of the same traffic sent at 866 Mbps.
What the percentage means
The total is the channel utilization of one AP with all listed devices active at their offered load simultaneously. It is a capacity figure for a single cell in isolation. It says nothing about whether the signal reaches the far corner. A figure above 100% means the devices are asking for more channel time than one AP can supply, which is why the tool then returns a higher access point count.
Why the threshold is 70% and not 100%
Utilization and user experience are not linear. Past roughly half load, waits for the medium get longer and more variable, so latency and jitter climb well before raw throughput drops. Voice and video degrade first, because they are sensitive to delay variation rather than bandwidth. Designing to a 70% ceiling leaves room for bursts, roaming and retries.
The cost ratio
Cost divides a group's share of channel time by its share of the traffic. A group above 1.0 consumes more airtime than its data contributes, like a slow client being sent the same megabits as a fast one. This is the comparison that identifies the client worth fixing: the higher the cost, the more capacity is freed per device upgraded.
How rates are derived
PHY rates come from the 802.11 MCS tables for the selected band, channel width, standard and spatial streams; signal quality selects the assumed MCS index. A MAC efficiency factor is then applied per generation to account for preamble, interframe spacing, ACKs, contention backoff and aggregation: Wi-Fi 4 ≈ 0.50, Wi-Fi 5 ≈ 0.60, Wi-Fi 6 ≈ 0.70, and a legacy 6 Mbps basic rate ≈ 0.40. The effective rate is the PHY rate multiplied by this factor.
Limitations
- Models one cell in isolation, with no co-channel or adjacent-channel neighbours.
- Overhead is modelled as a share of each transmission, not frame by frame.
- Retries are not modelled.
- MU-MIMO and OFDMA are not modelled, which understates a modern AP.
- Offered load is what a client wants to send, not a measurement of what it is doing.
- PHY rates are a snapshot, since real clients rate-adapt continuously as they move.
In order of value:
- Improve coverage so clients connect at higher rates. Rate is the divisor, so doubling it halves airtime.
- Move clients to 5 or 6 GHz, where wider channels and faster rates slash the time each transmission takes.
- Disable the lowest basic rates so management traffic and slow devices stop holding the channel.
- Address the specific slow device. The cost ratio above shows which one buys the most capacity back.
- Enable airtime fairness if your APs support it, so one slow client cannot starve the rest.