Each trading platform places a minimum amount by which a user can buy or sell a coin. In a few words, we cannot buy as much as we want, but our purchase should be above from a minimum value. Each platform has set its own minimum limits, which gradually and due to the latest rapid increase of users and transactions taking place, are increasing. This increase to these limits aim to prevent the so-called "spam-trades", namely micro transactions which are mainly carried out by trading bots (automated programs used for trading) which have the purpose to increase the volume of transactions in a market and creating an artificial mobility to attract investors.
It is very important for us to know the minimum limits a platform has set, since if we buy a coin from platform A in order to sell it on platform B, the quantity we buy from A should be in line with the limits set by B.
Examples of minimum trading limits:
0.00000500 BTC: TradeSatoshi
0.00001000 BTC: Bleutrade
0.00010000 BTC: Poloniex, CoinExchange, Nova Exchange, Yobit
0.00050000 BTC: Cryptopia
0.00100000 BTC: Bittrex
0.00200000 BTC: Binance