LoRa RF Packet Timing Utility

LoRa Airtime & Data Rate Calculator

Calculate LoRa symbol duration, symbol rate, nominal coded data rate, preamble time, payload symbols, total packet airtime and effective payload throughput from spreading factor, bandwidth, coding rate and packet configuration.

✓ SF5–SF12 ✓ LoRa Airtime ✓ Symbol Time ✓ Coding Rate ✓ Payload Throughput ✓ LDRO

LoRa Packet Configuration

● Ready

Spreading Factor Higher spreading factors increase symbol duration and generally increase airtime.

Bandwidth 125 kHz is commonly used for many LoRa and LoRaWAN channels.

Coding Rate More redundancy improves coding protection but increases packet airtime.

Custom Bandwidth

Bandwidth Unit

Payload Length PHY payload length in bytes supplied to the airtime equation.

Preamble Symbols Eight programmed preamble symbols are a common LoRa packet setting.

Header Mode Implicit mode removes the explicit payload header contribution.

Payload CRC Payload CRC contributes to the payload symbol calculation.

Low Data Rate Optimization Auto enables LDRO when symbol duration is at least 16 ms.

LoRa airtime model: packet airtime depends on PHY parameters, not simply payload bytes divided by a bit rate. The calculator applies the LoRa symbol and payload-symbol equations. Low Data Rate Optimization in Auto mode is enabled when calculated symbol duration is at least 16 ms.

LoRa Airtime & Data Rate Result Calculated

Total Packet Airtime —

Total Airtime —

Symbol Duration —

Symbol Rate —

Nominal Coded Bit Rate —

Preamble Time —

Payload Time —

Payload Symbols —

Total Symbols —

Payload Throughput —

LDRO —

Coding Rate —

Bandwidth —

Payload Airtime Share

0% — 100%

Parameter	Value	Unit / State	Calculation

Airtime Calculation Breakdown

—

What Is a LoRa Airtime Calculator?

A LoRa Airtime Calculator determines how long a complete LoRa packet occupies the radio channel. Packet airtime depends on spreading factor, signal bandwidth, coding rate, payload size, preamble length, header configuration, CRC and Low Data Rate Optimization.

Airtime is important for LoRa network capacity, battery-powered sensors, packet scheduling, collision probability and regulatory duty-cycle planning.

LoRa Symbol Duration Formula

LoRa uses chirp spread spectrum modulation. The duration of one LoRa symbol is:

Symbol Time
= 2^SF / Bandwidth

For SF7 at 125 kHz:

2^7 = 128

Symbol Time
= 128 / 125000

= 0.001024 seconds

= 1.024 ms

LoRa Symbol Rate

Symbol rate is the inverse of symbol duration:

Symbol Rate
= Bandwidth / 2^SF

For SF7 and 125 kHz:

125000 / 128
= 976.5625 symbols/s

Spreading Factor and Airtime

Increasing spreading factor increases the number of chirp states represented by each symbol but also increases symbol duration exponentially.

SF	2^SF	Symbol Time at 125 kHz
SF7	128	1.024 ms
SF8	256	2.048 ms
SF9	512	4.096 ms
SF10	1024	8.192 ms
SF11	2048	16.384 ms
SF12	4096	32.768 ms

LoRa Preamble Airtime

The LoRa preamble timing model includes the configured preamble symbols plus 4.25 additional symbols.

Preamble Time
= (Preamble Symbols + 4.25)
× Symbol Time

For an eight-symbol preamble at SF7/BW125:

(8 + 4.25) × 1.024 ms

= 12.544 ms

LoRa Payload Symbol Formula

The payload portion is calculated from the payload bytes and PHY settings. The commonly used LoRa time-on-air relationship is:

Payload Symbols =
8 + max(
ceil(
(8×PL - 4×SF + 28 + 16×CRC - 20×IH)
/
(4 × (SF - 2×DE))
)
× (CR + 4),
0
)

PL is payload length in bytes, CRC is 1 when enabled, IH is 1 for implicit header mode, DE is 1 when Low Data Rate Optimization is enabled, and CR uses values 1 through 4 for coding rates 4/5 through 4/8.

Total LoRa Packet Airtime

Payload Time
= Payload Symbols × Symbol Time

Total Airtime
= Preamble Time + Payload Time

This is why simply dividing payload bits by a nominal bit rate does not produce the correct LoRa packet time.

LoRa Coding Rate

LoRa coding rate adds forward-error-correction redundancy to the encoded packet. The common options are:

Calculator CR	Coding Rate	Code Factor
1	4/5	0.8
2	4/6	0.6667
3	4/7	0.5714
4	4/8	0.5

Higher redundancy generally increases packet duration because additional coded symbols must be transmitted.

LoRa Nominal Data Rate

A useful nominal coded information-rate expression is:

Bit Rate
= SF
× (Bandwidth / 2^SF)
× 4 / (4 + CR)

This describes modulation and coding characteristics. It is different from actual application payload throughput because packet headers, preamble and CRC consume airtime too.

Payload Throughput

The calculator separately reports effective payload throughput:

Payload Throughput
= Payload Bytes × 8
  -----------------
   Packet Airtime

This is often more useful when estimating how quickly a real sensor payload can be transported.

What Is Low Data Rate Optimization?

Low Data Rate Optimization, commonly abbreviated LDRO, changes the payload encoding behavior for long LoRa symbols to improve robustness against clock drift during long symbol periods.

The calculator’s Auto setting activates DE when the calculated symbol duration is at least 16 milliseconds.

SF11 / BW125:

Symbol Time
= 2048 / 125000
= 16.384 ms

Auto LDRO:
Enabled

Bandwidth and LoRa Airtime

Increasing bandwidth shortens every LoRa symbol when the spreading factor is unchanged.

SF7 / BW125:
1.024 ms per symbol

SF7 / BW250:
0.512 ms per symbol

SF7 / BW500:
0.256 ms per symbol

The available bandwidth settings depend on the radio transceiver and regional radio configuration.

Why SF12 Packets Take Much Longer

SF12 uses 4096 chirp positions per symbol compared with only 128 at SF7. At the same 125 kHz bandwidth:

SF7:
1.024 ms / symbol

SF12:
32.768 ms / symbol

32× longer symbol duration

A similar payload can therefore occupy the channel for dramatically longer at SF12.

Payload Size and Airtime

Increasing payload length eventually increases the number of required LoRa payload symbols. Because the payload calculation includes a ceiling operation, airtime often increases in discrete symbol groups rather than smoothly for every individual byte.

That means adding one extra byte does not always increase airtime, but at certain boundaries it causes another coded symbol block to be transmitted.

Explicit vs Implicit Header

Explicit-header mode transmits information describing the packet configuration as part of the LoRa packet. In implicit mode, the receiver must already know the required packet parameters.

IH = 0
Explicit Header

IH = 1
Implicit Header

The selected header mode changes the payload-symbol equation and therefore can change total airtime.

LoRa CRC and Airtime

When payload CRC is enabled, the packet contains additional error-detection information. The CRC setting is represented by the CRC term in the payload symbol calculation.

Disabling CRC can reduce the encoded packet size in some configurations, but the appropriate setting depends on the radio protocol and application requirements.

LoRa Airtime and Duty Cycle

LoRa airtime is commonly used as an input when analyzing regulatory duty-cycle limits. If a transmitter has an allowed duty-cycle percentage, the total transmission time within the applicable regulatory interval must remain within the permitted limit.

This page calculates packet time on air. It does not determine whether a specific transmission frequency, power, dwell time or duty-cycle schedule is legally permitted in a particular country or band.

LoRa Airtime vs LoRaWAN Airtime

The underlying modulation airtime mathematics is LoRa PHY timing. A LoRaWAN packet adds protocol fields before the LoRa PHY payload calculation is performed.

Therefore, when estimating a complete LoRaWAN transmission, enter the actual PHY payload length being transmitted rather than only the application data bytes if those differ.

LoRa Airtime & Data Rate Calculator FAQs

How is LoRa airtime calculated?

Calculate the symbol duration from spreading factor and bandwidth, determine preamble and payload symbol counts, then multiply those symbols by symbol duration.

What is the LoRa symbol-time formula?

Symbol time equals 2 raised to the spreading factor divided by signal bandwidth in hertz.

What is the LoRa symbol rate?

Symbol rate equals bandwidth divided by 2^SF and is the inverse of symbol duration.

Does increasing spreading factor increase airtime?

Generally yes. Symbol duration doubles each time the spreading factor increases by one while bandwidth stays constant.

Does higher bandwidth reduce LoRa airtime?

Yes, when the other settings remain the same, greater bandwidth reduces symbol duration.

What is SF7 at 125 kHz symbol time?

It is 1.024 milliseconds per LoRa symbol.

What is SF12 at 125 kHz symbol time?

It is 32.768 milliseconds per symbol.

What does coding rate 4/5 mean?

It is the lowest redundancy option in the commonly used LoRa coding-rate range represented by CR=1 in the airtime formula.

What is LoRa LDRO?

Low Data Rate Optimization modifies encoding for long symbol durations to improve robustness against timing drift.

When does this calculator automatically enable LDRO?

Auto mode enables it when the calculated LoRa symbol duration is at least 16 milliseconds.

Does payload size affect LoRa airtime?

Yes. A larger payload generally requires more encoded payload symbols and therefore more transmission time.

Why does airtime sometimes stay unchanged after adding one byte?

The LoRa payload-symbol formula includes a ceiling operation, so multiple nearby payload sizes can map to the same encoded symbol count.

Is LoRa nominal data rate the same as payload throughput?

No. Actual payload throughput is lower because packet airtime also includes preamble, header-related encoding and optional CRC overhead.

Can this calculator be used for LoRaWAN?

It can calculate the LoRa PHY airtime when you provide the correct PHY payload length and radio parameters used by the LoRaWAN transmission.

Calculate LoRa Packet Airtime

Estimate LoRa time on air, symbol timing, encoded data rate and effective payload throughput from spreading factor, bandwidth, coding rate, preamble, header, CRC and Low Data Rate Optimization settings.