Short answer
Who invented the microwave? Percy Spencer, an engineer at the American defense company Raytheon. In 1945, while working near an active magnetron, the device that generates microwaves for radar, he noticed that a candy bar in his pocket had melted. He tested the effect on popcorn and an egg, and Raytheon patented microwave cooking that same year.
Key takeaways
- The microwave oven was invented by Percy Spencer, an engineer at the defense company Raytheon, after he noticed in 1945 that a candy bar in his pocket had melted near radar equipment.
- He tested the idea with popcorn kernels, which popped, and an egg, which burst.
- Raytheon filed a patent for cooking with microwaves in October 1945; it was granted in 1950.
- The first commercial microwave oven, the Radarange, appeared in 1947: nearly six feet tall and weighing about 750 pounds.
- A compact countertop model arrived only in 1967, and by the mid-1980s more than half of US households had one.
The microwave oven is a rare case of an invention with a clear inventor, a clear date and a clear moment of discovery. It is also a good example of how a war technology can end up on a kitchen counter.
The engineer without a diploma
Percy Spencer was born in Howland, Maine, in 1894. He left grammar school at the age of 12 to work in a weaving mill, and joined the US Navy at 18 as a radio operator.
During the Second World War, Spencer and his colleagues at Raytheon produced large amounts of radar equipment, built around the magnetrons that generate microwaves. Over his career, he obtained more than 100 patents.
The melted candy bar
The story of the discovery is simple. In 1945, Spencer was standing near an active magnetron when he noticed that a candy bar in his pocket had melted.
He placed popcorn kernels near the magnetron, and they popped. He tried an egg, and it burst. The energy that radar sent out to detect aircraft could also heat food, quickly and from the inside.
From discovery to patent
Raytheon moved fast. On October 8, 1945, the company filed a patent for a microwave cooking process. It was granted on January 24, 1950.
The six-foot oven
The first commercial microwave oven, the Radarange, went on the market in 1947. It was nothing like a kitchen appliance: nearly six feet tall, weighing around 750 pounds and needing water to cool it. Sources give prices of $3,000 to $5,000, a fortune at the time.
It took about twenty years to make the microwave practical for homes. In 1967, Amana introduced the Radarange RR-4, the first compact countertop model, for $495. Adoption then grew steadily, and by the mid-1980s, microwave ovens were in more than half of all US households.
A short timeline
| Year | Event |
|---|---|
| 1945 | Spencer notices a melted candy bar near a magnetron |
| 1945 | Raytheon files a patent for microwave cooking |
| 1947 | The Radarange, the first commercial microwave oven, goes on sale |
| 1950 | The patent is granted |
| 1967 | The first compact countertop microwave oven, for $495 |
| Mid-1980s | More than half of US households own one |
Accident or discovery?
The microwave is often listed among “accidental inventions”, and the candy bar is the reason. But the accident was only the beginning. Spencer had to notice it, understand what had happened, test it and turn it into a device. The melted chocolate was luck; the oven was work.
Spencer died in 1970, and in 1999 he was inducted into the National Inventors Hall of Fame.
A very different accident, a glue that did not stick properly, led to another everyday object. See Who Invented Post-it Notes?, or explore Inventions & Discoveries.
Frequently asked questions
Who invented the microwave oven?
Percy Spencer, an engineer at Raytheon, after he noticed in 1945 that radar equipment had melted a candy bar in his pocket.
Was the microwave invented by accident?
The discovery was accidental, but the invention was not: Spencer tested the effect with popcorn and an egg, and Raytheon patented microwave cooking the same year.
When was the first microwave oven sold?
In 1947, as the Radarange, a machine nearly six feet tall that weighed about 750 pounds.
When did microwaves become common in homes?
After the first compact countertop model was introduced in 1967. By the mid-1980s, more than half of US households had one.