The Bill
Power BI is part of the Fabric ecosystem. Fabric is an end-to-end data platform, including ingestion, warehousing, outflows, and dashboarding, including Copilot for Power BI. The costing for Fabric involves you purchasing capacity units (CU), from F2 for 2, to F2048. Capacity units are measured in seconds. If you have 2 capacity units per second run, then you have 60 seconds available to you per 30 seconds of runtime. When I ran my workspace, I paid for 5 hours x 60 minutes / hour x 60 seconds / minute x 2 capcity units = 360,000 seconds, for a total of $1.80. But that’s not the full story.
Fabric bills Copilot at 100 CU seconds per 1,000 input tokens and 400 CU seconds per 1,000 output tokens. A request with 2,000 input tokens and 500 output tokens consumes 400 CU seconds, about 6.67 CU minutes. An average Power BI Copilot query in my instance ran about 1,500 CU seconds, though summaries have costed more. At the pay-as-you-go rate of $0.18 per CU hour, that’s roughly $0.075 per question. But the CUs come out of the same capacity pool that runs your Spark notebooks, warehouse queries, dataflows, and semantic model refreshes.
Regardless, you’re paying for fixed capacity, if you consume more than that then the service should throttle.
When you open a dashboard in Power BI or run a SQL query, the cost for that is spread out over the next 5 minutes to 24 hours. Copilot operations are classified as background jobs, so they get spread across 24 hours. This helps because it means the capacity you have running idle at 2am takes some of the cost of a burst of user queries at 2pm. This is a good thing.
That also means the 400 CU seconds from one query gets divided into roughly 16.67 CU seconds per hour across the next day. It’s also what makes the cost hard to notice until it accumulates. I ran my Fabric environment for 5 hours, but during that time, fabric was assuming that I would be running it for the next 24 hours.
If you have twenty queries a day from one user, 22 working days a month: about 660,000 CU seconds, 183 CU hours, roughly $33 in shared capacity consumption. Their Power BI Pro license costs $10. A team of ten moderate users on an F64 ($8,400/month) would put about 39% of the entire capacity toward Copilot alone. The remaining 61% handles everything else. The Capacity Metrics app is retrospective, not preventive.
The F2 made all of this visible because there was nothing else running. On a production F64, the same $17 of Copilot consumption would be a rounding error in a monthly bill that’s already four figures. Same cost. Same CUs consumed. Different signal-to-noise ratio.
Leave a Reply