Zabbix vs. PRTG: what the sensor model really costs

PRTG by Paessler AG is the default answer to the monitoring question in many German IT departments: quick to install, plenty of ready-made sensor types, a decent interface. Zabbix is the open-source alternative without license costs. The comparison comes down to three points: the per-sensor pricing model, the platform question (Windows core versus Linux), and what your environment will look like in five years (as of July 2026). For the comparison with Checkmk, see Zabbix vs. Checkmk.

Two very different models

To be fair up front: Paessler AG is based in Nuremberg - like Checkmk, PRTG is a product from the DACH region, with German support and a long track record. Both systems address the same core job: monitoring the availability and performance of servers, networks and services, raising alerts, delivering reports. The differences are not about credibility but about the model: PRTG is licensed per sensor and is subscription-only now; Zabbix is licensed under the AGPLv3, all features are free, hosts and metrics unlimited (license).

The sensor model explained

In PRTG, a sensor monitors exactly one aspect of a device: a ping, a CPU, a disk, a switch port, a Windows service. The official rule of thumb from the Paessler helpdesk: 5 to 10 sensors per server, 1 sensor per switch port; 500 sensors cover roughly 50 devices.

This is exactly where the cost dynamic lives: the sensor count grows faster than you expect at purchase time. Every additional disk, every VLAN interface, every service you want to watch counts against the license limit. Whoever starts with PRTG 1000 today will be discussing the upgrade to PRTG 2500 in two years - not because the environment doubled, but because the monitoring got more thorough. As a guideline, Paessler also recommends fewer than 5,000 sensors per core server (system requirements); very large environments therefore need multiple installations.

Zabbix counts differently: items collect as many values per host as you like, with no license limit ticking along. The question "can we afford this additional check?" simply never comes up - which in day-to-day practice leads to more thorough monitoring instead of rationed sensors.

The cost calculation

The list prices (as of July 2026, billed annually, in US dollars including on the German website, price list):

If you prefer not to host it yourself: PRTG Hosted Monitor costs $2,399 to $19,699 per year depending on the tier.

Cost example for 200 servers: By the official rule of thumb (5 to 10 sensors per server) you land at 1,000 to 2,000 sensors. PRTG 1000 only fits at the very bottom of that range and leaves no room for switches, firewalls and growth - realistically you need PRTG 2500, i.e. $8,904 per year, every year. With Zabbix, the license bill for the same environment is 0 euros - regardless of whether it later grows to 500 servers. To stay fair: Zabbix is not free of cost either, because platform and maintenance cost time or money. That full calculation is broken down in What does server monitoring cost?.

Windows core versus Linux

The second structural difference: the PRTG core server runs exclusively on Windows (Windows Server 2016 through 2025). Linux systems can of course be monitored, and for remote sites there is the Multi-Platform Probe, which also runs on Linux - but the central server itself always demands a Windows machine (system requirements). For Linux-heavy environments that means: you operate a Windows server, including its license and patch cycle, just for the monitoring.

Zabbix is Linux-native: server, proxies and agents run on the same distributions as the rest of your infrastructure, can be automated with the same tooling and fit into existing Linux operating processes. For distributed sites, both systems work with outposts - PRTG with probes, Zabbix with proxies that collect measurements locally and report them to the server in bundles. The structural difference persists here too: Zabbix proxies run on any common Linux distribution and cost no license. How deep the integration goes is illustrated by the official Proxmox template: Monitor Proxmox with Zabbix.

Migration path: from PRTG to Zabbix

The switch is not a big bang but an orderly four-step process:

1. Inventory: Review and export all devices and sensors in PRTG. This regularly reveals which sensors have accumulated over the years and are effectively obsolete - the migration is a good opportunity to clean up.
2. Mapping: Map PRTG sensors to Zabbix templates and items. Official, vendor-maintained templates exist for standard technologies (SNMP switches, Linux and Windows servers, HTTP checks, databases); special cases are rebuilt as custom items.
3. Parallel operation: Build the Zabbix environment, onboard the hosts and run both systems side by side for a few weeks. Compare alerts, tune thresholds, build trust.
4. Cutover: Switch alerting to Zabbix and let the PRTG subscription expire at the end of its term.

The honest verdict

PRTG is a well-maintained product with a fast start, and for small environments that permanently stay below a few hundred sensors, the list price is bearable. The larger and more dynamic the environment, the harder the sensor model works against you: more thorough monitoring leads straight to higher license tiers, and the Windows core remains a foreign body in Linux landscapes. Zabbix inverts the logic: the platform costs no license, more thorough monitoring costs no surcharge, and you only pay for operations - handled in-house or as a service.

How WZ-IT does it

We handle the complete migration path - inventory, template mapping, parallel operation, cutover - and the operations afterwards: as Managed Zabbix in your environment or as server monitoring as a service from 79.90 euros per month, with onboarding to our highly available Zabbix cluster and alerts delivered straight to your team. Whether the switch pays off for your sensor count is something we calculate in a free initial consultation.