Temperature matters. Be careful of measuring your fingers when you’re cold as they’ll measure smaller than at other temperatures.
Time is of the essence. Consider measuring your fingers later in the day as this is when they are at their largest.
Third time lucky. Experts recommend measuring your finger three times to ensure the correct ring sizing.
Shape matters. Wider rings typically fit a bit tighter, so you may need to consider the next size up to ensure it fits during the proposal.