Smart CPM explained, and when a fixed bid is better
How the auction ranks every bid by eCPM, how Smart CPM prices a win at one cent above the next bid, and how country floors fit in.
· 4 min read
Every time a visitor loads a page with an UluMob zone, the campaigns that can show an ad there compete in an auction. Knowing how that auction ranks bids and sets the price helps you choose between the two bid strategies, fixed and Smart CPM, and set a bid that wins without paying more than it has to.
Step one: every bid becomes an eCPM
Campaigns are bought in different ways: per thousand impressions (CPM), per click (CPC), per conversion (CPA) or per view for video. To compare them for the same visitor, the auction converts each bid to an eCPM, an effective price per thousand impressions.
- A CPM bid is already an eCPM.
- A CPC bid is multiplied by a click rate expected for the format, then scaled to a thousand impressions.
- CPA and CPV bids are converted the same way, with an expected conversion or view rate.
Those expected rates are set per format, not per campaign. A higher bid ranks higher, whatever the pricing model.
Step two: eligible campaigns are ranked
Before ranking, a campaign has to be eligible for this visitor and this zone. Its targeting must match, the zone must not be on its blacklist, its frequency cap and volume caps must not be reached, and its eCPM must be at least the zone's reserve price, if the zone has one.
The eligible campaigns are then sorted by eCPM, highest first. Campaigns with exactly the same eCPM are ordered at random, so a tie does not always favour the same advertiser. Before a winner is chosen, the auction also checks that its budget and balance can still pay; a campaign that has spent its daily budget is skipped and the next one takes its place.
Step three: the price
This is where the two strategies differ.
Fixed. You pay your bid. A $2.00 CPM bid costs $2.00 per thousand impressions whenever it wins.
Smart CPM. You pay one cent above the eCPM of the next campaign in the ranking, never more than your own bid, and never less than the zone's reserve or the country's floor for the format. Your bid becomes a maximum rather than a price.
A worked example, with illustrative numbers:
| Campaign | Strategy | Bid (CPM) | eCPM | Rank |
|---|---|---|---|---|
| Yours | Smart CPM | $2.00 | $2.00 | 1 |
| Campaign B | Fixed | $1.40 | $1.40 | 2 |
| Campaign C | CPC, converted | n/a | $0.90 | 3 |
You win. With a fixed bid you would pay $2.00. With Smart CPM you pay $1.41: the next eCPM plus one cent. If campaign B were not there, you would pay $0.91. If someone else bid $2.00 as well, you would pay $2.00, since the price never exceeds your bid.
When there is no other bidder at all, you pay the floor: the zone's reserve or the country floor for the format, whichever is higher, and never more than your bid.
Smart CPM is available for CPM pricing only. CPC, CPA and CPV campaigns always pay their bid.
Where country floors fit in
Floors apply to the bid you enter, not to the price the auction later charges. When you save a campaign, the panel checks:
- The campaign bid must be at least the highest floor among the countries you include.
- Each per-country bid you set on an ad must be at least that country's floor.
- If you do not include specific countries, the format's default floor applies.
Default floors, used where a country has no floor of its own:
| Format | Default floor |
|---|---|
| Popunder | $0.10 CPM, or $0.50 CPA |
| Banner | $0.05 CPM, or $0.50 CPA |
| Interstitial | $0.20 CPM |
| Domain redirect | $0.50 CPM |
| Video | $0.50 CPM, or $0.003 CPV |
| Telegram | $0.10 CPM, or $0.003 CPC |
| Push | $0.003 CPC, or $0.50 CPA |
| In-page push, native | $0.003 CPC |
Country floors, and the volume available in each country, are on the traffic volume page. Check them before you build a campaign that mixes expensive and cheap countries: a single campaign bid has to clear the highest floor among them, so per-country bids are usually the better way to cover both.
Setting a Smart CPM bid
Because your bid is a ceiling, set it at the most a thousand impressions are worth to you, not at the price you hope to pay. A practical way to get there:
- Take your target cost per conversion and your expected conversions per thousand impressions from earlier campaigns or from your tracker.
- Multiply them. That is the most a thousand impressions can cost before the campaign loses money.
- Set the Smart CPM bid at or a little below that number.
- Pass
{cost}in the destination URL so your tracker records what each impression or open actually cost, which under Smart CPM is often less than your bid.
If you have no data yet, start just above the floor and raise the maximum step by step while watching cost per conversion.
When a fixed bid is better
For the same bid, Smart CPM wins exactly the same auctions as a fixed bid and never costs more. The cases for a fixed bid are narrower than many buyers assume:
- You buy per click, per conversion or per view. Smart CPM only applies to CPM pricing, so these campaigns are fixed by definition.
- You need a flat, predictable price. Some buyers settle with an offer owner at a fixed cost per thousand, or plan budgets around one. A fixed bid keeps every impression at the same price.
- You are comparing tests. When you split-test landing pages or creatives on CPM, a fixed bid removes price variation from the comparison, so differences in result come from the page, not from the auction.
Outside those cases, Smart CPM is the sensible default for CPM campaigns.
Summary
- Every bid is converted to an eCPM and ranked; ties are broken at random.
- Fixed pays your bid. Smart CPM pays the next eCPM plus one cent, capped at your bid.
- Country floors apply to the bid you enter; use per-country bids when floors differ.
- Use fixed for non-CPM pricing, flat-price deals and clean tests.
To set up your first campaign with Smart CPM, create an account.