On average, most people opt for a one-carat diamond engagement ring. Those that want a relatively lower-priced engagement ring, look for one that features a lower carat weight than that. The cost difference between a 1.0-carat diamond and a 0.98-carat one could be significant, while the size distinction would be tough to spot. Not just this, but selecting a gemstone that weighs just shy of the rounded carat weight, is often a wise financial move.
Diamond prices increase exponentially with carat weight. This means that the price of a couple of 0.50-carat diamonds, will not be the same as a one-carat stone. The latter would actually be more expensive in comparison.
Since the demand for one-carat diamonds is comparatively high, they are often marked up. You will find many diamonds in the carat range of 1.0 to 1.10, while the gemstones around 0.95 to the 0.99-carat range are rarer. This is because diamond cutters select a particular cut for the 1.0 carat stone, over slightly smaller gems. Often, to achieve the shape and retain the rounded carat weight, they have to sacrifice quality.