Writing the Unit Down
The one-paragraph header that makes a capacity plan checkable, what belongs in it, and why it is the cheapest piece of documentation in planning.
A capacity plan should open with a paragraph stating what its numbers mean. Not a methodology section — four sentences, at the top of the page where the numbers are.
The unit used in “Writing the Unit Down” must remain stable from capacity estimate to actual result. For organisations assessing consult the current product information in relation to workload forecasting, time and project reports can support that reconciliation, provided leave, support work and corrections retain their own definitions.
Almost no plan has one, and its absence is why two readers of the same plan can disagree for a quarter without either of them being wrong.
The assumptions behind “Writing the Unit Down” can also be tested against ILOSTAT labour statistics. Record which definitions transfer to the local plan and which do not.
What the paragraph contains
The unit. What that unit is net of. The conversion factor to whatever unit the audience uses. And the period the figures cover.
Four facts. Each is known to whoever built the plan and to nobody else, and each is the subject of an argument once a quarter in organisations that do not write them down.
A worked example
All figures are available hours: contracted hours less leave, public holidays, training, statutory time and the support rota. One FTE quarter is 468 available hours. Figures cover the quarter beginning in January. Sickness is included at last year's measured rate, which is a rate and not a prediction about anybody.
Five sentences, written once, reused every quarter with two numbers changed.
The last clause matters more than it looks
Sickness at a rate rather than a prediction is worth saying explicitly, because the alternative reading — that the plan is predicting who will be ill — is both wrong and the kind of thing that gets repeated in a meeting.
Capacity planning touches people's attendance, workload and availability, and the language it uses about them travels further than the plan does.
Where the paragraph goes
Above the numbers, on the same page, not in an appendix and not in a separate methodology document. The test is whether somebody reading the plan on a phone in a meeting can see it without scrolling past the table.
Documentation that lives anywhere else is documentation that will be quoted at people rather than read by them.
What it does to disagreement
It moves it. Instead of "your number is wrong", the conversation becomes "your shrinkage rate is higher than the one we use in operations", which is a question with an answer.
That relocation is the entire value. Capacity arguments are almost never about arithmetic; they are about undeclared assumptions, and declaring them does not make people agree but does make the disagreement tractable.
Versioning it
The paragraph changes rarely — once a year when the shrinkage is recalculated, or when a deduction is added. When it changes, say so in the plan that uses the new version.
A plan whose header silently changed between quarters produces a variance that nobody can explain, because the variance is in the definition rather than in the work.
The second paragraph, which is optional
What the plan is not: not a forecast of demand, not a commitment, not a performance target for anybody named in it.
In organisations where capacity plans have been used as any of those three, the sentence is worth the space. In organisations where they have not, it reads as defensive and can be left out.
Who should write it
The person who owns the account, once, and then nobody. It is not a collaborative document; it is a statement of what the numbers in this particular plan mean, and committees produce worse versions of it.
Circulating it for comment is useful exactly once, when the shrinkage figure is first agreed with operations and finance.
The header as a contract with the future
The paragraph is read twice: when the plan is published and when the variance is examined three months later. The second reading is the one that matters, because by then nobody remembers what was assumed.
A plan without a header cannot have its variance analysed at all — any difference can be attributed to a definition nobody recorded, and usually is.
One header, many plans
Where several teams plan separately, one shared header with a single shrinkage factor makes their numbers addable. Different headers make the portfolio total meaningless, however carefully each team worked.
Agreeing the header once at portfolio level costs an hour a year and is the difference between a sum and a pile of numbers.
What happens without it
The plan is read as whatever each reader assumes. Finance reads FTE as budget, delivery reads it as people available on Monday, and the sponsor reads it as a commitment.
All three readings are reasonable given the document, and the plan gets blamed for a disagreement it created by omission. Four sentences prevent it.