Amos Mendenhall – Complete Biography, History, and Inventions

The practical calculator of Amos Mendenhall (© National Museum of American History, Washington, D.C.)

Amos Mendenhall – Complete Biography, History, and Inventions

Who Was Amos Mendenhall?

Amos Mendenhall was an American inventor that was recognized for attaining five US patents. He left a stamp on American history after he patented a practical calculator (US patent 67786) in 1867.

The headstone of Amos Mendenhall is in Buena Vista Cemetery, Winchester, Indiana. He shares a headstone with his niece, Leila Bell Mendenhall, who died only two days prior.

Early Life

Amos Cowgill Mendenhall was born on November 16, 1828, in Clinton County, Ohio, to Hiram Mendenhall and Martha Ann Hale. Amos had two sisters and seven brothers: Rowena, (1822-1887) and Martha, (b. 1826), Joseph Hale (1824-1908), Nathan, (b. 1830), Jacob Hale (1833-1885), John and William, twins, (born and died in 1835), Samuel H. (1836-1923), and James Hiram (1839-1909).

Quick Facts

Full Name
Amos Cowgill Mendenhall
November 16, 1828
April 10, 1909
Net Worth
Place of Birth
Clinton County, Ohio
Fields of Expertise
Practical Calculator, tricycle, bicycle, gold mining devices

In 1836, Mendenhall’s clan (Amos, together with his family and other families) moved from Clinton County, Ohio, to Randolph County, Indiana. Amos’s father started a fine farm on 400 acres of land before proceeding to erect a sawmill. Further, he created two grist Mills that were later moved on to a woolen factory.

There is very little information that referenced Amos’s early life. The most notable reference to his early life was in 1850, during the California Gold Rush. Amos and his father, Hiram, traveled to California to partake in the gold fields, in an attempt to recoup their previously lost family fortunes.

However, they were unlucky in their attempt and decided to erect a sawmill on the Sacramento River. This was operational until it was sold for a tangible sum of money before they departed to return home. Unfortunately, Hiram died of cholera on June 30 while on the shipboard in the Gulf of Mexico. 


Almost nothing is known about Amos Mendenhall’s career. Some sources suggest that he worked as a store manager, manufactured goods, farmer, and mechanic around Indiana after he returned home from their California Gold Rush adventure. It was believed that he invented all these patents during his days working as a mechanic.

What Did Amos Mendenhall Invent?

The Practical Calculator

The practical calculator of Amos Mendenhall (© National Museum of American History, Washington, D.C.)

In 1867, Amos Mendenhall of Cerro Gordo, Indiana, patented a practical calculator (US patent 67786). The patent model of the device (up to 1880, the US Patent Office required inventors to submit a model with their patent application) is still preserved in the National Museum of American History, Washington, D.C.

The practical calculator of Amos Mendenhall is a square metal box with overall measurements of 5.4 cm x 13 cm x 13.8 cm. The box has a boss in the center inside, in which the shaft of a cylinder is to turn.

The practical calculator of Amos Mendenhall is an adder with a brass box that has a rotating disc inset on the top. There are 100 small holes around the rim of the disc. Outside the disc, on the top of the box, is a circular ring numbered from 01 to 99, with a gap at 00. Outside of this are three rings of holes, with 100 holes in each ring. These holes are to be used to hold markers indicating digits carried when the disc makes full rotations. On the side of the box is a rotating multiplication table.

Amos Mendenhall proposed two methods for recording numbers over 99. The first was a set of nine holes around the edge of the fixed disc, into which the operator could place a pin. Whenever the rotating disc moved a full turn, the operator moved the pin up to the next hundreds digit. Mendenhall suggested a mechanism that would count the number of times the upper plate rotated, and hence give the hundreds place. If the operator rotated especially energetically and arrived at higher numbers, he suggested a system of pins to be used to represent thousands and higher places.

The practical calculator of Amos Mendenhall (© National Museum of American History, Washington, D.C.)

Other Works

Mendenhall not only patented the practical calculator which was his first, but he also took out patents for gold mining devices (#360713, granted April 5, 1887, and # 541912, granted June 11, 1895), a tricycle (#453151, granted May 26, 1891), and a bicycle (#740156, granted September 29, 1903).

For the gold mining devices, he invented Dredgers; Soil-shifting machines mechanically-driven with digging elements on an endless chain mounted on the floating substructure. 

Amos Mendenhall: Marriage, Divorce, Children, and Personal Life 


According to all available information garnered, Amos Mendenhall was never recorded to be married. 


Amos Mendenhall did not have any children.


Amos Mendenhall died on April 10, 1909, in Unionport, Ohio.

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Frequently Asked Questions

Who was Amos Mendenhall?

Amos Mendenhall was an American inventor and a holder of five patents which include gold mining devices, a tricycle, and a bicycle. He is widely known because of his practical calculator, which is still preserved in the National Museum of American History to this day. He was considered a good mechanic during his life.

What did Amos Mendenhall invent?

Amos Mendenhall patented the practical calculator (USpatent 67786) in 1867. Also, he is the holder of four more patents which include: gold mining devices (US360713 and US540997); tricycle (US453151); bicycle (US740156).

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