Mitochondria are tiny organelles within most eukaryotic cells. Mitochondria act as energy factories for a cell, turning various forms of sugar into ATP, a source of chemical energy mots of the cell can use. Since mitochondria are found in such diverse life forms as plants, animals and protists, there is some variation in their size, but certain generalities hold up well.
The most obvious way to measure a mitochondria is the organelle's physical size. A human mitochondron is typically one to two micrometers, but may be as large as seven micrometers. This means that a human mitochondrion is 0.000039 to 0.000079 inches. If you prefer metric, this means a 0.0001 to 0.0002 centimetres, or 0.001 to 0.002 millimetres.
Mitochondria (and chloroplasts in plants) contain DNA of their own, separate from the cell's nucleus. This DNA is called mitochondrial DNA, abbreviated mtDNA. Since all DNA contains information, some prefer to judge its size based on the amount of data it stores, like a CD or a flash drive. A single human mitochondrial genome contains 37 genes, 16,569 base-pairs or about 16 kilobytes of data.
A typical human mitochondrion's size is about the same as an average-sized bacteria, like E. coli or S. aureus. This is much smaller than an typically-sized human cell, which is usually around 30 micrometers. If a human was shrunk down to the size of a mitochondria. a cell would appear to be the size of a football field. This means that about 1000 to 2000 mitochondria could fit on a 2-millimeter pin head.
Since most eukaryotes have mitochondria, there is considerable diversity among the size and shape of mitochondria. They generally range from .5 micrometers to ten micrometers. In general, plants have larger mitochondria than animals. Animals, at the outside, can have mitochondria up to 16 kb of data in their mitochondria, while plants' mtDNA can contain as much as 200-2400 kb. Also, certain types of stress like oxygen deprivation, starvation and free radical poisoning can enlarge mitochondria in a condition called megamitochondria.