Izzy (Wheaton, Missouri) on 12/24/2025

One gram of borax contains approximately 11.3% boron by weight, which equates to 113 milligrams of boron. This percentage is consistent across multiple sources, including chemical analyses and product descriptions. The exact amount can vary slightly depending on the specific form of borax (e.g., decahydrate, pentahydrate), but 11.3% is a widely accepted value for sodium tetraborate decahydrate, the most common form. Therefore, in 1 gram of borax, there is about 0.113 grams, or 113 mg, of elemental boron.