Carat weight is the weight of the diamond measured in carats. The word "carat" is taken from the carob seeds that people once used in ancient times to balance scales. Don't confuse "carat weight" with "karat," the method of determining the purity of gold.

One carat is divided into 100 "points," so that a diamond of 75 points weighs 0.75 carats. Carat weight is the most obvious factor in determining the value of a diamond. But two diamonds of equal carat weights can have very different prices, depending on their quality. Diamonds of high quality can be found in all size ranges.

First, determine your budget. One general rule of thumb when buying a diamond engagement ring is "two months salary." This is just a guideline, it's not carved in stone and your first consideration should be what you can comfortably afford, not what the diamond industry or a jeweller tells you. If you have a set budget, explore all your options and you'll find that there is a wide range of diamond carat weights and qualities available in your price range.

Deciding on carat size is really about striking a balance between size and quality. If your intended prefers larger jewellery items, and you are working within a budget, you can still find a larger diamond of excellent quality gem by selecting one which is graded slightly lower in terms of colour and clarity.

Things to bear in mind are:

If your recipient is very active or not used to wearing jewellery, she may find herself bumping or scratching her new ring. Consider a smaller size diamond or a setting that protects a larger diamond from getting knocked against furniture.

Also keep in mind that the smaller the finger, the larger the diamond will appear. A 1.00 carat diamond solitaire looks much larger on a size J finger than a size P.

Finally, if a large carat weight is important to you, yet you're working within a budget, consider a diamond with a good cut, SI1–SI3 clarity, and an I or J colour grade.