What is a US league?
A US league is three miles or 15,840 feet. The word comes from the Late Latin leuca, a Gaulish measure traditionally taken as an hour's walk.
The league was used for the distance between towns and for a ship's run at sea. The mile and the kilometer replaced it, and it now mostly turns up in older books. A US league of three miles is about 4.83km.
What is a kilometer?
A kilometer is 1,000 meters, or about 0.621 miles. 'Kilo' is the Greek-derived prefix for a thousand. It is the unit for road distances nearly everywhere except the US and UK, which still use miles.
A kilometer is about 3,281 feet or 39,370 inches. At a walking pace of 5km/h it takes about 12 minutes to cover.
Going from kilometers to meters just means moving the decimal point three places. A mile has to be broken into 1,760 yards or 5,280 feet first, and neither of those is a round number of anything.