What does the tracker SIM data calculator estimate?
A tracker sends small messages all day. Each one carries a few dozen bytes of position and status, plus the headers of the network protocol, and the operator counts every byte, often rounded up. The total decides which SIM plan you need and what the fleet will cost each month.
This calculator turns your settings into a monthly figure. The Monthly usage tab gives megabytes per device and for the fleet and shows where they go. The SIM plan tab fits the figure to plan sizes and shows what billing rounding adds. The What if tab shows the effect of other intervals and protocols, and finds the shortest interval that stays inside a plan you choose.
Why interval and overhead decide the data
- Moving data follows the interval. A position every 15 s is twice the data of a position every 30 s. Parked heartbeats do not change.
- Small packets are mostly headers. A 60-byte position report travels with about 80 bytes of IP, TCP and acknowledgement. The header can be larger than the data.
- Opening a link is expensive on TLS. A TLS handshake can take several kilobytes. Keep the link open and it is paid once, not for every report.
- Billing rounds up. A session of 300 bytes on a 10 KB step is billed as 10 KB. This matters when every report is its own session.
Inputs you need
| Input | Where to find it | Tip |
|---|---|---|
| Payload, extra fields, heartbeat | Device protocol document or a packet log | The starting values are typical. Replace them with real sizes. |
| Report and heartbeat intervals | Device settings or your platform | Use the values the vehicles actually run, not the factory defaults. |
| Moving hours and active days | Shift plan or past trip reports | Use ignition-on time, not shift length. |
| Protocol and overhead | Device and server configuration | Pick TCP, UDP or TLS, then edit the overhead if you measured it. |
| Billing step and megabyte definition | SIM contract or tariff sheet | If it is not written, ask the supplier. |
| Plan sizes | Your supplier's price list | The tool uses common steps from 5 MB to 1,000 MB. |
How it is calculated
Everything is counted in bytes per device, then shown in MB. The default megabyte is decimal, 1,000,000 bytes. Switch to binary, 1,048,576 bytes, if your operator uses it.
Reports per day
Bytes on the wire
Header sizes come from the IP, TCP and UDP specifications: RFC 791 (20 bytes), RFC 9293, which replaced RFC 793 (20 bytes without options), and RFC 768 (8 bytes). Source and date checked: 3 November 2026. The acknowledgement, the connection setup and the TLS handshake are typical values you can edit.
A day and a month
An idle day has no moving hours, so it carries heartbeats only. When the device opens a link for each report, every report adds the setup bytes and is rounded on its own.
Worked example: 50 trackers on a 30-second interval
- Moving day: 10 hours at 30 s is 1,200 position reports of 140 bytes, which is 168,000 bytes. 14 parked hours at 300 s is 168 heartbeats of 96 bytes, which is 16,128 bytes. Two connections of 240 bytes add 480 bytes. Raw day: 184,608 bytes. Rounded to 1 KB per session, the billed day is 186,368 bytes.
- Idle day: 288 heartbeats of 96 bytes plus 480 bytes of setup is 28,128 bytes, billed as 28,672 bytes.
- Month: 26 × 186,368 + 4 × 28,672 = 4,960,256 bytes. With a 25% margin that is 6.2 MB, and one 1 MB update a year adds 0.08 MB. Total: 6.28 MB per device.
- Plan and fleet: the 10 MB plan holds it with 63% used. For 50 devices the fleet uses about 314 MB a month.
- Another interval: at 60 s the same device uses 3.55 MB, which is 43% less.
Reading your results
- Monthly data per device includes your margin and the yearly updates. It is the figure to compare with a plan.
- Where it goes shows whether positions, heartbeats, connection setup or rounding dominate. Start with the largest bar.
- Fits, tight, too small mark each plan size. Tight means 80% to 100% of the plan, which leaves little room for a bad month.
- Billing rounding added is the extra the step costs you. If it is large, look at how often the device opens a link.
- Shortest interval is the fastest reporting that stays inside your target plan with the current settings.
Common mistakes
- Counting only the payload. Headers and acknowledgements often double a small report.
- Forgetting parked time. Heartbeats run all day and on days with no movement.
- Using factory intervals. Many fleets change the interval in the field. Use what the vehicles run now.
- Ignoring the billing step. A 10 KB step can multiply the data of a device that opens a link for every report.
- Leaving out updates and extras. Firmware, settings and other services add data on top of positions.
Assumptions and limits
The result is an estimate. Real traffic depends on signal quality, retries, server acknowledgement behavior, roaming and the services running on the device. The month has 30 days. All starting packet sizes, overheads and plan sizes are typical values, not measurements from a Tracom device, and they can be edited. Measure one week of real use in your SIM portal and update the inputs before you buy a plan.