Every placement has a field called units per USD. It does one thing: turn the dollars an offer earns into the currency your users understand. Earn $0.35, set the rate to 1,000, and the user sees 350 coins.
That is the entire mechanic. The decision is harder than the mechanic.
Work backwards from what a coin buys
The rate is meaningless on its own. 1,000 per dollar sounds generous and 10 sounds stingy, but both are the same wall if your prices move with them. What matters is the relationship between what an offer pays and what a user can buy with it.
So start at the other end:
- Pick the reward your users actually want — a $5 gift card, a skin, a week of premium.
- Decide how long a motivated user should take to earn it. A day of steady effort is a reasonable target for a first payout; a month is a wall nobody finishes.
- Look at what your offers pay. On most walls the middle of the catalogue is somewhere between $0.20 and $2.00 per completion, with a long tail above that.
Now the arithmetic works itself out. If your $5 reward should take roughly five decent completions, and a decent completion pays about $1, then five dollars of earnings has to buy that reward — and the rate is whatever makes your price tag read cleanly.
Round numbers, always
1,000 per dollar. 100. 10,000. Never 850, never 1,250.
Users do arithmetic on your currency whether you want them to or not, and a round rate makes every offer on the wall legible at a glance: a 35-cent offer is 350 coins, and the next one up is obviously worth twice as much. A rate of 850 turns the same wall into a page of numbers nobody can compare.
Round rates also survive the thing that eventually happens to every economy: you change the prices. Doubling every price in a 1,000-per-dollar economy is a five-minute job. Doing it in an 850-per-dollar economy means every number in your shop is now something like 1,487.
Decimals: only if you need them
The placement has a decimals shown setting alongside the rate, from zero to five. Most walls should leave it at zero.
The exception is a low rate. If one dollar buys one credit, then a $0.35 offer is 0.35 credits, and rounding that to a whole number makes every small offer worth nothing at all. That is what the decimals are for. If you are running a rate of 1,000, whole numbers are correct and decimals just make the card noisy.
One rule either way: the setting is exact. Choose two decimals and every reward prints as 5.00, not 5. A list where some rows have decimals and some do not looks like a rendering fault.
Write the number the way your users write it
There is a number format setting next to the decimals, and it is not cosmetic. A German player reading 1,250.50 Coins reads one and a quarter coins — the comma is a decimal point where they live, and nothing in the number tells them otherwise.
Pick the format your audience uses. It applies to the card, the balance in the header and the history page together, so the wall is consistent wherever the user looks.
The mistake that costs you users
Changing the rate after launch.
Every user who earned at the old rate now holds a balance that means something different, and there is no version of that conversation that goes well. If you have to change it, change your prices instead — the rate stays, the reward costs more or less, and nobody's balance is retroactively reinterpreted.
If you genuinely must change the rate, do it before you have users, or accept that you are running a currency reform and announce it like one.
What we store
The rate used is written onto every conversion at the moment it happens, along with the dollar amount and the currency amount. Changing your rate later cannot rewrite what a user was paid last week — the history is fixed at the time it was earned, which is the only way a support conversation about an old reward can ever be settled.