It is shown that Henry's law constants can be experimentally determined by comparing headspace content of compounds with known constants to interpolate the constants of other compounds. Studies were conducted over a range of water temperatures to identify temperature dependence. The Henry's law constants for a suite of mostly labeled compounds intended for use as internal standards were determined, and these internal standards were then used to determine the constants for 90 compounds. This approach was found to correlate well with the average of published values for the compounds in the study (0.99) and had a very good correlation (> 0.99999) when compounds had measurements from more than two sources.