Two questions, because there are two conductors
A utility bill sees the whole service and nothing inside it. Twelve months of the landlord's demand records establish the existing load on the service under NEC 220.87, and the new tenant's load added at 125% of that measured demand answers whether the service can carry the fit-out.
The tenant's equipment lands on one feeder and one panel, and the bill cannot see either. Whether that feeder has room is a separate question with a separate answer, and it is established by recording that feeder for 30 days, under the same section, or by calculation where the suite has never operated and there is nothing to record.
How the new tenant's load is counted
Per its own article, because the new load is not installed yet and cannot be measured. Motors under Article 430, with the largest at 125% and the rest at 100%. Fixed electric heating under Article 424. Air conditioning at its rated-load current under 440.6. Continuous loads, anything that runs for 3 hours or more, at 125% on their own circuits. Equipment with no article of its own at nameplate.
A commercial kitchen is the case the code is kindest to. Table 220.56 applies a demand factor to kitchen equipment that reaches 65% at six or more units, on the understanding that a kitchen never runs everything at once, and the calculation never drops below the sum of the two largest pieces. A restaurant fit-out that looked impossible at nameplate is often comfortable once the table is applied, and the study applies it.
What the lease should wait for
The feeder answer. A landlord who promises a suite a certain capacity on the strength of the service having room has promised something the bill cannot support. The service can have hundreds of amps spare while the feeder to that suite has none, because the feeder was sized for the last tenant. Thirty days on the feeder settles it, and a sealed study is the document both sides of the lease can hold.
When the answer is no
Then it is no on the feeder, or no on the service, and the study says which. A feeder can be upgraded without touching the service, which is a different job at a different cost from a service upgrade, and knowing which one is needed before the lease is signed is most of the value of asking.
Questions people ask
Can the landlord's bills answer whether the suite has room?
For the service, yes: 12 months of demand records establish its existing load under NEC 220.87. For the feeder to the suite, no. A bill sees the whole service and nothing inside it, so the feeder is recorded for 30 days instead.
How is a restaurant's kitchen equipment counted?
Under Table 220.56, with a demand factor that reaches 65% at six or more units and a floor of the sum of the two largest pieces. A kitchen never runs everything at once, and the code assumes so.
What if the suite has never operated?
Then there is no existing demand on that feeder to measure, and the feeder side is calculated under Article 220. The service side can still be measured from the landlord's records.
Can a feeder be upgraded without a service upgrade?
Yes, where the service has room and the feeder does not. It is a different and usually smaller job, and the study says which of the two is actually the constraint.