eCPM calculator

Cost per click is what a click actually cost, from the report rather than from the bid. A bid is a ceiling and is usually not the price.

Click-through rate is the share of impressions that produced a click on the same buy. This is where the figure most often goes wrong, because rates are quoted from memory and each platform publishes more than one. Use the rate that matches the clicks being priced: if the cost per click was calculated on link clicks, use the link click-through rate.

Impressions is optional. Supplying it turns the derived rate into a volume check — the clicks those impressions should have produced and the spend they should have cost.

A thousand impressions at a 1.4 per cent click-through rate produce fourteen clicks. Fourteen clicks at 0.85 each cost 11.90. That is the effective cost of a thousand impressions on this buy, and it was never negotiated with anybody.

The shortcut is worth remembering: effective cost per thousand equals the cost per click multiplied by the click-through rate multiplied by ten. The relationship runs in every direction, which is why these three numbers can never be read independently. Halving the click price while halving the click-through rate leaves the effective cost exactly where it was.

Impressions are the only unit every buy shares. A cost per click and a cost per view are prices for different events and cannot be compared; both, however, consume inventory, and the effective cost per thousand says what that inventory cost. That makes this the right figure for a question about media efficiency — am I paying more for the same attention than I was last quarter, or than I am on another platform.

It is the wrong figure for a question about outcomes, and the mistake is common enough to name. Search inventory almost always carries a much higher effective cost per thousand than a feed, because a small number of impressions in front of people who typed the query produce a high click rate. That is not overpaying; it is paying more per thousand for attention with intent behind it. Ranking placements by this number alone systematically prefers the cheapest inventory available, which is exactly the inventory that produces the fewest outcomes.

The honest use is to compare like with like: the same placement across periods, the same audience across platforms, or a per-click buy against a per-thousand buy for the same objective and surface.

The second and third outputs exist because a derived number should be checked against something real.

Given 750,000 impressions at the same two rates, the buy should have produced 10,500 clicks and cost 8,925. If the report says the campaign served 750,000 impressions and the invoice says something materially different, one of the inputs is wrong — and in practice it is nearly always the click-through rate, either because a different click definition was used or because the rate was quoted from a different period than the spend.

That check is worth running before the effective cost is used in any comparison, because the figure is entirely derived. It carries the error in both inputs and shows none of it.

Mixed placements. A campaign serving across several surfaces has one blended click-through rate and one blended click price, and the effective cost that comes out describes no individual placement. Break the report out before deriving anything.

Different click definitions. A cost per click computed on all clicks and a click-through rate computed on link clicks produce an effective cost that is wrong in a direction nobody can see.

Impression counting. Served, viewable and measured impressions are different events, and platforms differ in which they report. Two effective costs built on different impression definitions are not comparable, whatever the arithmetic says.

Auction dynamics. The effective cost is an average over a period during which the auction was moving. A figure derived across a month that included a retail peak describes a market that no longer exists.

Use it as a price index rather than a performance metric. Track it over time for the same placement and audience: a rising effective cost with a stable click-through rate means the market is charging more for the same attention, which is a budget conversation. A rising effective cost driven by a rising click-through rate means the creative is working and the platform is happy to serve it, which is the opposite conversation.

Use it across platforms only after checking that the impression and click definitions match, and use the cost per result rather than this figure whenever the decision is about where the money should go. This number prices the inventory. It has never once said whether the inventory was worth buying.