What is minimum order size?

The minimum order size is about 1 USD in value for all trading pairs.

For specific amount for a given pair, you may check it with  Market Info API. 

Go to API Document at the bottom of Gate.io website and you can see it. 

Example:

 https://data.gateio.co/api2/1/marketinfo

Return data example:

    # Request
    GET: https://data.gateio.co/api2/1/marketinfo
    # Response
   {
        "result": "true",
        "pairs": [
                      {
                            "eth_btc": {
                                "decimal_places": 6,
                                "min_amount": 0.0001,
                                "min_amount_a": 0.001,
                                "min_amount_b": 0.0001,
                                "fee": 0.2,
								"trade_disabled ": 0
                            }
                      },
                      {
                            "zec_btc": {
                                "decimal_places": 4,
                                "min_amount": 0.0001,
                                "min_amount_a": 0.0001,
                                "min_amount_b": 0.0001,
                                "fee": 0.2,
								"trade_disabled ": 0
                            }
                      }
            ]
    }