Minimum order and quantity step: why the bot did not buy exactly 10 USDT
An exchange does not accept just any number. Every pair has a minimum, a quantity step and a price step — and every order a bot sends is fitted to them.
Three limits of a pair
- Minimum amount: the exchange will not take an order worth less. It differs from pair to pair and exchange to exchange.
- Quantity step: a coin cannot be bought in “any amount”, only in multiples of the step. On one pair the step is a tiny fraction of a coin, on another whole coins.
- Price step: an order’s price is a multiple of its own step too.
- The app shows these numbers under the chosen pair in the bot form.
Why it did not buy exactly the amount you set
You set a rung’s amount in USDT, and the exchange counts in coins. The bot divides the amount by the price and rounds the quantity down to the step — never up, or the rung would spend more than it was given. So a 10 USDT rung may buy for 9.97, say. The rest is not spent and stays in the account.
Why the minimum needs a margin
Because of rounding down, an amount right at the minimum can end up under it once rounded — and the exchange refuses. That is why the app will not let a rung sit exactly at the minimum: it asks for a small margin and names the smallest amount it will take.
A fee in coins, and “dust”
On a buy, an exchange often takes its fee in the coin you bought. You bought 0.00033 of a coin and 0.00032967 arrived. Only a multiple of the step can be sold, so 0.00032 goes and 0.00000967 stays. No order can sell that remainder by itself: it is smaller than a step.
The bot remembers the remainder and adds it to the same rung’s next sale. Once the remainders make a whole step, it is sold. So the account holds at most one step per rung, not a step more with every trade.
Exchanges call such crumbs “dust” and usually let you convert it by hand. If you do, the bot will not count the coins as missing.
What it means in practice
- The quantity in a sell order can be slightly less or slightly more than what was bought. That is rounding and remainders, not an error.
- On a pair with a large quantity step, a small rung buys noticeably less than its amount. The smaller the rung, the more it shows.
- If the exchange refuses orders for their size, make the rung’s amount larger.
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