The central billing element for both cellular and Wi-Fi is the Data Operation:

• Each publish, subscribe, function, or variable consumes one Data Operation regardless of size
• The data has a maximum size of 622 to 1024 bytes of UTF-8 characters; see API Field Limits
• Stored data, such as Tracker geolocation data, consume one Data Operation per location point saved¹
• Certain retransmissions, as described below

The following do not count against your Data Operations limit:

• Over-the-air firmware updates do not count against your Data Operations limit
• Internal events such as device vitals (beginning with "particle" or "spark") do not count against your Data Operations limit
• Acknowledgements, session negotiation, keep-alives etc. do not count against your Data Operations limit
• Webhooks and server-sent-events (SSE) themselves do not count against your Data Operations limit, but the triggering event or response could
• Particle cloud API calls do not count against your Data Operations limit

¹You will receive warnings by email, and as a pop-up and in the Billing & Usage tab in the console at 70%, 90%, and 100% of the allowable data operations. In the Free Plan you will have an opportunity to upgrade to the Basic plan. In the Basic plan, additional blocks can be added to allow for more data operations.