Most of the hosting here does not meter transfer. The economy plans do, and that is exactly why they cost less. Each one carries a monthly allowance instead: 10 GB, 25 GB or 50 GB, matched with 512 MB, 1 GB and 2 GB of NVMe storage.
What transfer is, and what it is not
Transfer is the total size of everything your site sends out to visitors over a month: the HTML, the stylesheets, the scripts, the fonts and above all the images. It is not the disk allowance, which is a separate figure for what the account stores, and it is not a limit on how hard the site is allowed to work. The processor and memory on an economy plan are the same two cores you get on the standard range.
Working out your own figure
Take the weight of one page as a browser reports it, multiply by the pages an average visitor looks at, and multiply again by the visitors you expect in a month. A tidy page with resized images is around one megabyte on a first visit and much less on the next, because the stylesheet and the fonts are already cached.
So a thousand visitors reading three pages each is a few gigabytes, not tens of them. The same site with an unresized photograph on every page is the one that finds the ceiling.
Leaving room
Estimate, then leave half. Not because the estimate is wrong, but because the things that move it are the ones nobody plans: a page that gets linked somewhere, a crawler reading the whole site, one image that was never resized on a page that turns out to be popular. A site that lands inside half its allowance in a normal month has a plan that survives an unusual one.
If you are close to the line
Two changes reduce the figure more than anything else. Resize images on upload, which usually halves it on its own and makes the site faster at the same time. And put a content delivery network in front of the site: it serves the static files from its own network, so they never come out of your allowance at all.
If neither is enough, the answer is the plan rather than the tuning. Our web hosting range starts one step up and does not count transfer, and the difference in price is small compared with the cost of watching a counter every month.
Who these plans are for
A personal site, a landing page, a small business site whose audience is measured in hundreds, a staging copy of something else: anything whose weight you control and whose traffic you can predict. For those, paying for unmetered transfer you will never use is paying for a number.
They are the wrong plan for a shop running a sale, for anything serving video or large downloads, and for a project whose traffic you are hoping will grow quickly.