Server size calculator
Sizing a server from what you already know: answer ten questions about the workload and get a starting RAM and vCPU band, the planning assumptions printed beside the result, and a verdict on whether to load test before you commit.
Undersizing hurts at peak; oversizing bills every month. Answer ten questions about the workload and get a starting band to provision against, with the assumptions and the load-test warning shown alongside.
By Sam Moreton
Researched
Calculator
Assumptions
- Each concurrent PHP worker is planned at 64-128 MB of RAM.
- Without a peak figure, peak concurrent users are estimated at one per 10,000 monthly visits, minimum 2.
- One in four peak concurrent users is planned to be waiting on an uncached page at the same moment.
- Cached share of requests: 80% mostly cached, 50% mixed, 20% mostly dynamic.
- Baseline per site on one small server (web server, PHP pool floor, database, object cache): WordPress 0.8-1.2 GB, WooCommerce 1.0-1.6 GB, Laravel 0.7-1.1 GB, other PHP 0.6-1.0 GB.
- Database working set above the baseline: 0.25-0.5 GB at medium intensity, 0.75-1.5 GB at high.
- A queue or background worker is planned at 0.25-0.5 GB on top of the web pool.
- Admin and editor activity above the baseline: 0.1-0.25 GB at medium, 0.25-0.5 GB at high.
- Growth headroom multiplies the top of the band only: none x1, modest x1.25, doubling x2.
- High sensitivity to slowness or downtime raises the floor of the band by 25%; it does not add redundancy, a single server stays a single point of failure.
- vCPU is planned at one core per 2 GB of RAM, band edges rounded up.
Formula vv0.1 / last reviewed 2026-10-09
Undersizing a server hurts at peak, in front of everyone. Oversizing hurts on the first of every month, for as long as you let it run. The calculator above takes what you already know about the workload and hands back a starting band: a RAM range, a vCPU range, and a verdict on whether a load test should come before you commit.
Who this is for
Anyone about to provision or resize a server for a workload they can describe: a WordPress site with traffic you can read off analytics, a WooCommerce shop heading into a sale, a Laravel app with a queue behind it, a small pile of sites you want on one box. If you can estimate monthly visits and guess how many people arrive at once, you have enough to run it.
How to read the band
The floor is where you can provision today. The ceiling is where growth and peak load are likely to push you, given the buffer you chose. Sit near the floor when the traffic estimate is solid and a slow page now and then survives being seen. Sit near the ceiling when a launch, a sale or a mailing list can multiply arrivals without warning.
Every constant the model uses is printed under the result, so you can argue with it, and arguing with it is the point. If you already run a server and know your real per-site footprint, your number beats the planning baseline. The Cloudways server size guide picks the sizing question up from here.
What it cannot know
The model sees concurrency and cache mix. It cannot see your plugin list, and the gap between a lean WordPress install and one carrying a page builder plus forty plugins is most of a small server. It cannot see spikes either: one good link on a quiet Tuesday can outdeliver a month of ordinary traffic. Page weight, query shape and cache hit ratio all live outside the form, which is why the answer is a band and never a single number.
When to trust it
Trust the band for content sites and shops whose traffic you can name from analytics. Pad it when the site is unlaunched and the traffic is a guess, or when downtime costs more than the server does. In those cases treat the result as a hypothesis and load test before launch; the calculator says so in its own output when the workload profile calls for it.
Where to go next
The Cloudways review shows what sized servers cost in practice, from a real monthly bill. If the size question is settled and the money question is open, the VPS vs managed TCO calculator prices your own hours into the decision. And once the server exists, the WordPress capacity estimator answers the reverse question: how many sites the box you just sized will carry.
FAQ
Why a range instead of one number?
Because the inputs are estimates, and a single figure would pretend otherwise. The floor is a safe place to start, the ceiling is where growth and peak load push you, and a load test tells you where in between your workload actually sits.
Does this pick a hosting plan for me?
No. The calculator answers in gigabytes and cores, so it works against any host that grades plans by RAM. Match the band to the plan pages you are weighing before committing to a tier.