Hermann Einstein (also known as Hermann Moos) was born in Buchau, Württemberg to his parents Abraham Einstein (1808–1868) and Helene Moos (1814–1887), who had married in Buchau in April 1839. The family were German Jews. He had three brothers (August Ignaz, Heinrich and Jakob) and two sisters (Jette and Friederike).

At the age of 14 Hermann attended the secondary school in the regional capital Stuttgart and was academically successful. He had a strong affection for mathematics and would have liked to study in this or a related area. But as the financial situation of the family opposed further education, he decided to become a merchant and began an apprenticeship in Stuttgart.