Your engagement ought to fit easily - not excessively close, but not excessively free by the same token. The ideal ring fits free to the point of sliding over your knuckle and tight enough so it can't tumble off your finger.
To observe your ring size, you can utilize James Allen's internet ring sizer or demand a free plastic ring sizer. Continue to peruse for tips on the best way to quantify your finger size and ensure that you buy a ring that fits perfectly.