In meringue, sugar is a structural ingredient as well as a sweetener. A quantity of sugar close to the weight of the egg whites produces a soft meringue that spreads easily; when the sugar is twice the weight of the egg whites, the meringue becomes firm and dries into a crisp texture in the oven. Set the ratio by weight, not volume, because one egg white weighs about 30 grams and varies from egg to egg.
Sugar does three jobs at once in meringue. It sweetens the foam, stabilizes it by tightening the protein network, and binds water to regulate drying in the oven. That is why changing the sugar ratio changes the entire character of the meringue, not just its sweetness. A meringue made with less sugar is lighter but more fragile; it deflates quickly and weeps. Meringue with a lot of sugar produces a heavy, glossy foam that holds its shape for a long time. For that reason, the amount of sugar in a meringue recipe is not a number to adjust freely based on how sweet you like it.
In practice, there are 2 basic ratios. When the sugar weight is close to the egg-white weight, the result is soft meringue; meringues spread over desserts, spread with a spoon, and cooked briefly use this ratio. When the sugar is increased to twice the weight of the egg whites, the result is dry meringue; this is how meringues that are dried in the oven for hours and become crisp confections are made. Intermediate ratios give intermediate textures. Pavlova falls between these 2 extremes; it is made so the outside is like dry meringue while the inside stays like soft meringue.
Measure by weight. An egg white weighs about 30 grams on average, but the weight varies with egg size; that is why a recipe using 3 egg whites yields a different weight each time. Put the egg whites in a bowl and weigh them, then calculate the sugar based on that weight. Cup and spoon measures are unreliable for this, because the size of the sugar crystals and how tightly they pack can change the measurement. After weighing the egg whites, subtract the bowl’s weight; otherwise the calculation will be off from the start and you will add too much sugar.
The type of sugar also affects the result. Fine-grained sugar dissolves faster and produces a smooth foam; coarse crystals may still be undissolved when whipping is finished, which can make the meringue weep. Do not use powdered sugar on its own, because its starch makes the foam heavy; it is generally used together with some of the granulated sugar. If using coarse sugar, you can pulse it briefly in a food processor to make it finer. If using powdered sugar, add it toward the end of whipping, after the granulated sugar has dissolved.
If you want to reduce the ratio, understand what you will lose. With less sugar, meringue is less sweet but also less stable; it colors more quickly in the oven and collapses as it cools. Do not reduce the ratio when making dry meringue. In soft meringue, a small reduction can be tolerated, and the mixture can be balanced by whipping it a little longer. Overwhipping also makes matters worse; once the foam loses its gloss and becomes lumpy, adjusting the ratio will not save it. That is why you should try reducing the sugar in a single small batch first, not a large trayful.