Enter the bytes passed to the radio, then compare the same packet at each spreading factor. The timeline separates preamble time from payload and coding.
One packet, from the first preamble symbol to the end of the payload.
28 payload symbols · 32.77 ms per symbol · low-data-rate optimisation on
Payload bytes range from 1 to 255. A spreading-factor change may also change receiver sensitivity.
2.198% transmit time at your interval. Retries and receive windows are separate.
Packet airtime
1,319ms
SF12, 125 kHz, coding rate 4/5. Low-data-rate optimisation on.
Check the values to see a result.
One transmission only. Receive windows, retries and regional restrictions are not included.
Tsymbol = 2^SF / BWTpacket = (preamble + 4.25 + payload symbols) × Tsymbol
20 PHY payload bytes occupy 1,319 ms at SF12.
Tip: LoRaWAN application bytes are not the complete PHY payload. Include the actual MAC headers, options and integrity code passed to the radio.
A small sensor message can occupy the radio channel for tens of milliseconds or more than a second. The spreading factor, bandwidth and coding rate matter as much as the number of bytes. Compare them with the same packet before choosing a reporting interval.
This tool implements the SX1276-style LoRa packet equations for SF7–12 at 125, 250 and 500 kHz. It is a PHY timing calculation, not a LoRaWAN network-capacity or regulatory compliance assessment.
PL = bytes passed to the radio
For LoRaWAN, an application payload is wrapped in protocol fields before transmission. Count the complete actual radio payload, including MAC options when present. Do not add the LoRa explicit PHY header to PL: its contribution is represented separately by the equation.
Tsymbol = 2^SF / bandwidth
At SF7 and 125 kHz one symbol lasts 1.024 ms. Low-data-rate optimisation is selected automatically above 16 ms per symbol, matching the supported settings. The receiver must use compatible settings.
Tpacket = (preamble + 4.25 + payload symbols) × Tsymbol
Payload symbols are quantised by the coding block ceiling. Adding one byte does not always increase airtime; crossing a block boundary does. The programmed preamble excludes the 4.25-symbol term already added by the model.
Transmit fraction = packet time / start-to-start interval
The result covers one packet. Retransmissions, acknowledgements, receive windows and other devices occupy additional time. If a packet is longer than the requested interval, that schedule cannot be met.
One symbol is 1.024 ms. The programmed preamble plus 4.25 symbols takes 12.544 ms, and 43 payload symbols take 44.032 ms. Total airtime is 56.576 ms, displayed as 56.58 ms. One packet every 60 seconds occupies approximately 0.0943% of the time.
Packet airtime 56.58 ms Open in the calculator
Low-data-rate optimisation is enabled. A symbol lasts 32.768 ms and the packet takes 1,318.912 ms, displayed as 1,319 ms. This is about 23.3 times the SF7 airtime, before any retransmissions.
Packet airtime 1,319 ms Open in the calculator
No. Airtime is the transmission duration of one radio packet. Scheduling, queueing, receive windows, acknowledgements and retries add latency.
No. It is a transmit-time fraction at the entered interval. Applicable sub-band rules, channel access methods, dwell-time restrictions and shared traffic require a separate regional assessment.
Payload coding rounds to whole blocks of symbols. Several adjacent payload sizes can occupy the same number of blocks.
No. The supported model deliberately excludes SF6 special handling, LR-FHSS and FSK. Check the exact radio datasheet for those modes.