OFDMA Efficiency Calculator
Compare 802.11ax OFDMA against single-user transmissions: resource units per channel, users per TXOP and the airtime saved.
About OFDMA Efficiency Calculator
OFDMA splits a channel into resource units so several clients are served in one transmission, paying the preamble, contention and acknowledgement overhead once instead of once per client. Each client gets a narrower slice, so its payload takes proportionally longer, and the saving comes entirely from amortising the fixed overhead. OFDMA only pays off for small frames from many clients — the exact profile of voice, telemetry and IoT traffic — and for a handful of large downloads it makes things slightly worse.
Formula
OFDMA Efficiency
resource units = data subcarriers ÷ RU size; OFDMA airtime = ceil(clients ÷ RUs) × (fixed overhead + frame airtime ÷ RU's share of the channel).
- resourceUnits
- Parallel sub-channels available in one transmission
- ruShare
- Fraction of the channel width one RU occupies
Worked example
With the default values below, OFDMA Efficiency Calculator returns Airtime Saved vs Single-User of 63.7%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Channel widthone of 20 MHz, 40 MHz, 80 MHz, 160 MHz
- 80 MHz
- Resource unit sizeone of 26-tone RU, 52-tone RU, 106-tone RU, 242-tone RU, 484-tone RU, 996-tone RU
- 106-tone RU
- Clients with data queuedaccepts 1–500 clients
- 24 clients
- Airtime for one frame at full channel widthaccepts 1–5,000 µs
- 30 µs
- Fixed overhead per transmissionaccepts 10–1,000 µs
- 100 µs
Results
- Airtime Saved vs Single-User
- 63.7%
- Resource Units per Channel
- 9
- Users Served per TXOP
- 9
- OFDMA Airtime for the Whole Group
- 1,132 µs
- Single-User Airtime for the Whole Group
- 3,120 µs
Step by step
- 1Values used
- 2OFDMA Efficiency
- 3Airtime Saved vs Single-User= 63.7
- 4Resource Units per Channel= 9
- 5Users Served per TXOP= 9
- 6OFDMA Airtime for the Whole Group= 1,132 µs
- 7Single-User Airtime for the Whole Group= 3,120 µs
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is OFDMA Efficiency calculated?
resource units = data subcarriers ÷ RU size; OFDMA airtime = ceil(clients ÷ RUs) × (fixed overhead + frame airtime ÷ RU's share of the channel). OFDMA splits a channel into resource units so several clients are served in one transmission, paying the preamble, contention and acknowledgement overhead once instead of once per client. Each client gets a narrower slice, so its payload takes proportionally longer, and the saving comes entirely from amortising the fixed overhead.
Why does OFDMA Efficiency matter?
OFDMA only pays off for small frames from many clients — the exact profile of voice, telemetry and IoT traffic — and for a handful of large downloads it makes things slightly worse.
What values do I need to enter?
This calculator takes 5 inputs: Channel width, Resource unit size, Clients with data queued, Airtime for one frame at full channel width, Fixed overhead per transmission. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.