Divako · LoRaWAN
How many devices fit one gateway cell?
Type in your fleet and read back the EU868 airtime it uses, whether every device stays inside the 1 % duty cycle, and what share of reports one coverage area can be expected to deliver. Everything runs in your browser; nothing is sent anywhere.
What one gateway cell delivers
Fits comfortably Fits, little headroom Does not fit Needs about – gateways
Room to grow, add alarms or lose a few dB of margin. Growth, an alarm storm or a worse SF mix will tip it over. Plan a second coverage area or a longer interval. Theoretical: a circle per gateway on flat ground. Terrain, masts and buildings move the real number; a pilot or the Divako network planner replaces this estimate. Per-device duty cycle. Devices at the highlighted SF transmit more than regulation allows. Coverage. Too many devices sit at SF10 and above; a gateway closer to them lowers their SF and frees airtime. Collisions. The mix is fine but the cell is full; split it into more coverage areas or report less often.
About – of – devices get each report through; about – are lost to collisions. (–)
About – of – alarms arrive within the window. (–)
Assuming all devices are within one gateway's reach. Enter the area above if they are spread out.
Coverage: – cells to cover – km² with a usable radius of about – km.
Reports expected to arrive: –. Share of all scheduled uplinks received, same-SF collisions only.
Limiting factor: None. The fleet fits inside one cell at this target. Area. The ground to cover, not the airtime, sets the gateway count. Each cell needs its own gateway; overlapping gateways do not add capacity. Per-device duty cycle. Devices at the highlighted SF transmit more than regulation allows. Coverage. Too many devices sit at SF10 and above; a gateway closer to them lowers their SF and frees airtime. Collisions. The mix is fine but the cell is full; split it into more coverage areas or report less often.
1 % duty cycle: Every SF in the mix stays under 36 s of airtime per hour. At least one SF exceeds 36 s per device per hour. Lengthen the interval or shrink the payload; adding gateways does not help.
No radio network delivers 100 %. Above 99 % plan retries, store-and-forward on the device and a measured delivery deadline rather than more gateways.
| SF | Devices | Airtime per message | Airtime per device per hour | Load per channel | Delivered |
|---|---|---|---|---|---|
| SF7 | |||||
| SF8 | |||||
| SF9 | |||||
| SF10 | |||||
| SF11 | |||||
| SF12 |
Estimate only. Random transmission timing, no retries, no downlinks, no external interference, no capture effect. Real networks differ; a pilot with RSSI and SNR readings replaces these presets. Counts frames received at the gateway radio; forwarding, backhaul and network-server losses are not included.
How it is calculated
Three formulas, all standard. The page applies them to your numbers; nothing is tuned to make Divako look good.
Assumptions
- EU868, 125 kHz bandwidth, coding rate 4/5, 8-symbol preamble, CRC on, low-data-rate optimisation at SF11 and SF12.
- 13 bytes of LoRaWAN framing on top of your application payload; no MAC commands piggy-backed.
- Unconfirmed uplinks, spread randomly in time. No retries, no downlinks, no join traffic.
- All devices share one gateway coverage area. Gateways that hear the same devices share the same spectrum.
- Only same-SF collisions are counted. Different SFs are treated as fully separate, which is optimistic.
- The 1 % duty cycle applies to the default sub-band shared by 868.1, 868.3 and 868.5 MHz: 36 seconds of airtime per hour per device.
- Usable cell radius assumes an ordinary outdoor gateway with an omnidirectional antenna of a few dBi mounted about 15 m up, and devices allowed up to SF12. Open ground 3 km, town 1.5 km, basements 1 km, chambers under lids 0.7 km. A directional antenna, a taller mast or flat terrain reaches further; a pilot replaces these bands.
Airtime per message: Semtech LoRa modem formula from payload, SF, bandwidth and coding rate.
T = (8 + 4.25) × T_sym + N_payload × T_sym
Load per channel at one SF: devices × messages per hour × airtime ÷ (channels × 3600).
G = N × (60 / interval) × T ÷ (channels × 3600)
Delivered share at one SF: e^(−2 × load), the pure-ALOHA collision model.
P = e−2G
| SF | Airtime | Messages per device per hour at 1 % | Messages per hour one 8-channel cell carries at 5 % load |
|---|---|---|---|
| SF7 | 72 ms | 500 | 20 000 |
| SF8 | 134 ms | 269 | 10 800 |
| SF9 | 247 ms | 145 | 5 800 |
| SF10 | 453 ms | 79 | 3 200 |
| SF11 | 987 ms | 36 | 1 460 |
| SF12 | 1 810 ms | 19 | 795 |
What this page cannot tell you
Which SF each device actually lands at. That depends on where the gateway stands, what the meter sits under and how much margin the installer left. Run a pilot, read the SF distribution off the network server, then come back and type it into the custom mix.
Frequently asked
Why does adding a gateway not raise the numbers?
A second gateway that hears the same devices receives the same collisions. It adds coverage and reception diversity, not spectrum. Capacity grows when the second gateway serves devices the first one did not, which is what the 'separate coverage areas' figure counts.
What does 95 % report completeness mean in practice?
On average one scheduled uplink in twenty is lost to a same-SF collision. Devices that report hourly and keep a readings buffer recover most of those on the next uplink, which is why the 'heard at least once an hour' figure is higher.
Can I enter more than 51 bytes?
Not here. 51 bytes is the largest application payload SF12 allows in EU868. Devices at SF7 and SF8 can send up to 222 bytes and SF9 up to 115, but a calculator that let you mix those limits would silently break SF10 and above.
Do the presets come from real networks?
They are rounded shapes from municipal water-meter rollouts on Divako: a high mast over open ground pulls most devices to SF7 and SF8, a town centre spreads them out, and basements and chamber lids push a fifth of the fleet to SF11 and SF12. Your own distribution replaces them after a pilot.
Next step
Send us the device list. We sketch the gateways.
The calculator stops where coverage starts. With your addresses, meter positions and candidate masts we model link margin per device in the Divako network planner and return a placement with the SF mix it produces – in about 30 minutes.