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/plus plan. In the basic/plus plans, additional blocks can be added to allow for more data operations.