Capacity Planning
Definition
Capacity planning is the exercise of forecasting resource use and lining it up against what you have bought. For a static site the resources are few and countable: how many gigabytes you are storing, how many go out per month, how many requests that involves, and what the peak rate looks like as distinct from the average. The arithmetic is direct — average page weight multiplied by expected views, plus file size multiplied by expected downloads. A plan usually states its limits as a storage quota and a bandwidth limit, sometimes with a request count alongside, and the job is to be sure neither is close to being reached in a bad month rather than a typical one. Headroom is the part people skip: planning to sit at 95 per cent of an allowance means the first busy week takes you over it.
Why It Matters
Hitting a limit is worse than paying for the next tier up. Depending on the provider, going past an allowance either stops the site serving, throttles it, or quietly bills the overage, and the first two happen at the busiest moment rather than a convenient one. The sums are easy enough to be worth doing: a 2 MB page at 100,000 views a month is roughly 200 GB of transfer, which settles the plan choice on its own. Running the numbers once a quarter also catches drift, because page weight creeps up as images and embeds get added, and the cost per gigabyte only becomes visible when something multiplies it.
How It Works
Start from what you have: current storage in gigabytes, the last three months of transfer, and the busiest single day in that window. Work out average page weight from a handful of representative pages — the browser's network panel gives the transferred total per load — and note the size of each download people actually take. Multiply by a realistic view count, then multiply again by a peak factor for the worst plausible month; two to three times the average is a sensible starting assumption for anything with public exposure, and more if you are planning a launch or expecting a traffic spike. Add growth for whatever you will publish before the next review. Compare the total against the plan's allowances and decide in advance what the response to exceeding them is: a larger plan, smaller files, or a hard cap that stops serving.
Real-World Example
A local authority publishes planning documents at consultations.99helpers.site: about 6 GB of PDFs, growing by 400 MB a quarter. Transfer runs around 25 GB a month, but in the month a contentious application opens for comment it reaches 140 GB. Planning against the average would have put them on an allowance that failed in exactly the week the documents mattered most. Sizing against the peak instead, and re-exporting the largest PDFs at screen resolution, keeps them comfortably inside it.
Common Mistakes
- ✕Planning from the monthly average — both the bill and the limits are set by the peak, and a public site's peak is routinely several times its mean
- ✕Counting page views and forgetting downloads — one 30 MB file taken a few thousand times can exceed everything the pages transfer in a year
- ✕Never revisiting the numbers after launch — page weight grows quietly as images, fonts and embeds accumulate, and a forecast goes stale within a couple of quarters
Related Terms
Traffic Spike
A sudden, large rise in visitors or downloads over a short window — usually hours, sometimes minutes. It is what happens when a link is posted somewhere popular.
Cost per Gigabyte
The unit price a host charges for a gigabyte of something — most often storage held for a month, or data transferred out to visitors. The two are separate numbers and are easy to confuse.
Egress Fee
A charge for data leaving a provider's network — the bytes sent out to visitors when they load your pages or download your files. Data coming in the other direction is usually free.
Storage Quota
A storage quota is the total volume of data your account may hold at any one moment. It is a standing measurement of what sits on disk, and downloading a file does not change it.
Bandwidth Limit
A bandwidth limit is the total volume of data a host will send out on your behalf in a billing period, usually a month. It counts what leaves, not what is stored, so a tiny file can exhaust it and a huge one may never touch it.
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