Concentration / Osmolarity Calculation

I need help figuring out how to do the correct calculation with the problem below:

"Run a serial dilution with another, safe, household kitchen chemical. You will need to look up the molecular weight of the compound, and the weight of 1 tsp for that preparation of the compound. The density listed on sites such as Wikipedia will not account for air spaces between the grains of the solid so instead,the weight of 1tsp of the solid must be determined empirically. Alternatively, you can use kitchen scale of you have one. Once you know the weight of the chemical, calculate the concentration of an isotonic solution (what osmolarity should this be?). Start at twice the concentration of the isotonic solution and testing it for lysis."

The first solution I made was about 0.9% NaCl by adding 6 g of NaCl to 2.8 cups of water (per lab guide). How many grams of sugar do I need to add to 2.8 cups of water for it to be isotonic to the NaCl solution?