# IoT data usage calculator

Estimate how much mobile data a device uses in a month, and what that means across a fleet. The figure counts what the mobile network meters: your payload, plus the protocol headers, security handshakes, keepalives and reconnects that travel with it.

Per device, per month

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## How the estimate is built

The calculator counts bytes as a mobile network meters them: whole IP packets, in both directions. Units are decimal (1 MB is 1,000,000 bytes) and a month is 30 days, so every figure can be checked by hand.

- **Each message** is your payload plus the IP and TCP or UDP headers, the TLS or DTLS record overhead, the protocol's own header, any reply (an MQTT PUBACK, an HTTP response, a CoAP acknowledgement) and, over TCP, the acknowledgement packet.
- **Each connection** adds a DNS lookup, the TCP handshake and close, the security handshake and any protocol setup such as MQTT CONNECT. A device that opens a new connection for every message pays this every time, which is often the largest part of the bill.
- **Keepalives** are counted for MQTT when the gap between messages is longer than the keepalive interval.
- **Firmware and file downloads** are added in full for the month, not spread as a percentage.
- **Tariff rounding**, where a tariff rounds each data session up to a billing increment, adds half an increment per session on average.

Every overhead is an editable assumption with a stated default, not a typical figure for any device. Replace them with measurements from a representative device before sizing a tariff; the worked method is in [How to estimate IoT data usage](https://netavo.com/insights/iot-data-usage).

The calculator is open source: [netavo-gds/iot-data-usage-calculator](https://github.com/netavo-gds/iot-data-usage-calculator) on GitHub.

## Connect the fleet

Our multi-network IoT SIMs run on all four UK networks, with private access to your systems by IPsec, cloud interconnect, MPLS or L2TP.

[IoT & mobile data](https://netavo.com/services/iot)

[Work with us](https://netavo.com/work-with-us)

Source: https://netavo.com/tools/iot-data-usage-calculator