To add up on Denny's answer, the density of a solution of sugar and water is linear in the range we use in homebrewing (e.g. between 0.9 and 1.2). (see graph below [0] where concentration in wt% is equivalent to degree Plato)

[![density vs concentration][1]][1]

Using this graph, you could make a sugar solution with known density by adding sugar into water. E.g. a 5°Plato (5 wt%) solution would roughly be 5g of sugar in 95g of water.


> [0] https://www.engineeringtoolbox.com/density-aqueous-solution-organic-sugar-alcohol-concentration-d_1954.html

  [1]: https://i.sstatic.net/x38ZF.png