Lab · Capacity and load
Four Kinds of Number
Separate the size of a plan from the demand on a meter. Six worked examples make capacity, commitments and load easier to compare.
Capacity describes size. Load describes use. Sort six illustrative figures, mostly in megawatts, then explore how time turns power into energy.
Read the explanation
These are worked examples, not real facility disclosures. Six illustrative figures sort into four kinds: design or capacity, operating now, commitment and measured load.
Design or capacity: a 100 MW campus plan; the 40 MW capacity of a separate, completed building; and a 200 MW plan for two campuses. A whole size does not tell you how much is in use.
Operating now: the first 20 MW phase of the illustrative 100 MW campus has entered service. It is 20 per cent of the plan, not a statement of electricity being consumed.
Commitment: 75 per cent of the separate 40 MW building is contracted, equivalent to 30 MW. A commitment is not yet a load.
Measured load: an illustrative meter reading of 12 MW. This is the only card that represents electricity being drawn at a moment. The accompanying worked series is 3, 5, 7, 10 and 12 MW at monthly observations, not a real meter record.
Rate or total: a megawatt (MW) is a rate, how fast electricity is used or can be supplied. A megawatt-hour (MWh) is a total, a rate added up over a period. The illustrative 12 MW is a rate; 12 MW held for 24 hours gives 288 MWh. The IEA estimated that data centers worldwide used 485 TWh in 2025 (Key Questions on Energy and AI, April 2026), an annual total. A steady 10 MW for 24 hours gives 240 MWh; for 12 hours, 120 MWh. A site at 6 MW overnight and 10 MW by day has the same 10 MW peak but uses 192 MWh in a day.
A design can take years to fill, a commitment is not yet a load, a load reading is one moment, and a total depends on time. Each needs its date. The scenario figures illustrate these distinctions; they are not market estimates.
Behind the model
Assumptions
- All six figures in round 1 are original worked examples. They do not describe any reported campus, customer contract or measurement.
- Each figure is filed under the kind that best matches its wording. The 20 MW phase is also a capacity; it is filed as operating because the scenario says this part of the campus has entered service.
- The separate 40 MW building is complete. Its whole capacity is filed as design or capacity; the scenario does not say how much electricity it is using.
- The 75 per cent commitment belongs to that 40 MW building. The 12 MW meter reading and five monthly readings are separate illustrations, not evidence of the building’s consumption.
- The 485 TWh figure is an IEA estimate for 2025, not a meter reading. The average rate divides the year’s total by 8,760 hours and is rounded to two significant figures.
- The steady 10 MW load, and the day of 6 MW before 06:00 and after 18:00 with 10 MW in between, are the magazine’s worked examples (page 9), not real sites.
- Each chart row has its own scale. Connecting monthly observations does not establish the load between them.
Sources
- Issue 01: worked examples on pages 6, 9 and 69 to 83
Data Center Edition · 29 October 2026 - Key Questions on Energy and AI, executive summary
IEA · April 2026
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