There are a few environmental and physical factors that should be taken into consideration before deciding on the size of the ring you want to buy, but remember that when it comes to guessing your partner's ring size, guess on the large side as it's easier to size a ring down.

Keep in mind the average ring size range for women is between 9 and 14 (India), while sizes commonly range from 17 to 22 (India) for men. If you have no other information available, it's best to choose between these ranges.

An ideal time to measure their finger size is in the evening. Most people's fingers tend to be at their largest in the evening and smaller in the morning. Measuring your partner's finger size in the evening will guarantee a comfortable fit.

Fingers tend to react to temperatures, and can change size depending on the weather. The cold winter air will shrink fingers while the opposite happens in summer or when it's warm and humid. Avoid measuring finger size outside in the very cold or very hot.

Other factors can cause fingers to grow such as exercising, water retention, pregnancy, ageing, and arthritis. Weight loss and low temperatures can cause fingers to decrease in size.

Thicker ring bands (larger than 6mm) will fit tighter. It is advised to always go for half a size up when purchasing a thicker band, for the ring to be comfortable.