Advertising pays for this site. There is no other revenue and no plan for one. No accounts to upsell, no premium tier, no data to sell. That makes the ad layout a design decision worth explaining, because the obvious layout and the right one are different.
The obvious layout puts an ad at the top of the page, where it is seen first and paid best. Every incumbent in this category does it, which is why using them feels like tunnelling through a billboard to reach a calculator.
What the top slot is actually worth
It pays more than the others for a measurable reason rather than a vague one. Display inventory is bought against a viewability standard: an impression counts when at least half the ad’s pixels have been in the viewport for at least one continuous second. A slot that is on screen the instant the page paints clears that bar for essentially everybody. A slot below the tool clears it only for the people who scroll.
On a page whose whole purpose is to answer one question inside one screen, a great many people never scroll. That is the trade stated plainly: we build the layout that means they do not have to, and then we are not paid for the part of the page they never reach.
The geometry makes the choice for us in any case. A phone offers somewhere around 600 to 700 pixels of usable height once the browser’s own chrome is subtracted. A mobile leaderboard takes 50 of those and a medium rectangle takes 250, so putting either above a calculator pushes the calculator between 50 and 250 pixels down a screen that also has to hold a heading, two inputs and an answer. The rule is not squeamishness about advertising. There is not room for both, and one of the two is why the visitor came.
The rule and the price
The rule is simple: no ad above the tool, ever, and the tool usable without scrolling on a phone. Each page carries a fixed, small inventory; one small banner below the tool, one rectangle after the supporting content, and a tall unit beside it on desktop. Nothing is placed automatically. The slots live in the template, so how many ads a page carries is a decision made once rather than by a script at request time.
Every slot reserves its exact height in advance. That is arithmetic rather than politeness. Cumulative Layout Shift scores how much of the viewport moved and how far it went, so a 250-pixel ad dropping into a space reserved at zero, with content underneath it, is usually enough to fail the 0.1 threshold on its own. Reserving the height means the page is the same shape before the ad arrives and after.
That has a visible cost and we take it. Slots do not fill every time. Nobody’s do, and when one goes unfilled the reserved space stays reserved. There is a blank rectangle in the page. The alternative is collapsing the slot after a timeout, which produces exactly the layout shift the reservation existed to prevent, so the hole stays.
The other things we are not doing
The list is longer than the placement rule, and each item on it costs something real.
The embed route carries no advertising at all. When one of these tools is framed on somebody else’s site it loads no third-party script, sets no cookie and touches no storage, which is the only honest way to put a tool on a page you do not control, and which means embeds earn nothing and cost bandwidth. They exist because a tool that answers the question inside the paragraph is more useful than a link, not because the arithmetic favours them.
The internal rating never appears on a page and never goes into structured data as an AggregateRating. Star ratings in a search result raise click-through and we do not have them. In fairness, the honest version of that cost is smaller than it sounds: search engines have restricted self-serving review markup for years, but the rule would stand either way, because a rating a publisher awards itself is not information.
There is no interstitial, no countdown before the tool appears, and nothing that pins itself to the bottom of a phone screen while you scroll. Those are among the formats the Coalition for Better Ads found least tolerated, and Chrome filters advertising on sites that use them, so it is only fair to say that this particular restraint is partly enforced by somebody else, and that we would have kept the rule anyway.
And the number of tools here never appears in a headline, a navigation label, the footer or a 404 page. A count like that is a claim about us. Somebody arriving from a search for a unit conversion is not interested in us.
What is honest about the rest
The ad script is third-party code and it is comfortably the heaviest thing on a tool page. Our own JavaScript is budgeted under 100 KB gzipped and the tool itself is usually a fraction of that; the advertising is not ours, is larger, and sets cookies. Pretending otherwise would be treating a layout rule as though it were a privacy policy, and it is not one.
What the rule buys is narrower than that and more durable. Pages that do not move rank better and are less irritating to use, and a visitor who was not ambushed comes back the next time a number needs converting. A site meant to outlast the incumbents can afford the patient version of that trade. A site that needs the money this quarter cannot, which is most of why the incumbents look the way they do.