A tigress (female tiger) in a national park in India. Tigers are the largest cats on Earth.
Identifying the big cats
Of the forty cat species in the world, there are four to ten that are considered "big cats," depending on whose definition is being used. What's funny is that the strictest definition, listing only four species, leaves out one species that is larger than number four on the list.
Here are the ten largest cats on Earth:
1. Tiger - native to Asia, the Bengal subspecies is the largest.
2. Lion - native to Africa, plus there is a small population in Asia, in India.
3. Jaguar - found in the Americas.
4. Mountain lion - also called the cougar or puma, found in the Americas, and erroneously left off some "big cats" lists.
5. Leopard - native to Africa and Asia.
6. Cheetah - found in Africa, and there is also a small population in Asia, in Iran.
7. Snow leopard - Central Asian high mountain areas.
8. Eurasian lynx - found throughout most of Europe and Asia, but not tropical areas or the Arabian Peninsula.
9. Sunda clouded leopard - a separate species from the clouded leopard, and found on the islands of Borneo and Sumatra.
10. Clouded leopard - Southeast Asia and Southern China.
After sharing some information about big cats, photos of each of these ten species are shown below.
Lions are the second-largest cats after tigers, although they are taller than tigers. Photo was taken in Tanzania, in Africa's Serengeti region.
Which ones can roar?
Tigers, lions, jaguars, and leopards can roar. The above-mentioned shortest list of big cats, which includes four species, is these – although on average, mountain lions are larger than leopards and therefore don’t deserve being left off the list. Mountain lions, however, cannot roar.
Which ones can purr?
Here’s a fact not too many people know, because scientists were wrong about this for quite some time. It turns out that all cats purr, even lions and tigers. Perhaps it was difficult to get close enough to find that out!
Fastest runner, best jumper, and best swimmer
Everyone knows cheetahs are the fastest land animal on Earth, reaching 70 mph (113 km per hour). This is about 20 mph (32 km per hour) faster than the second-place cat, which may be either lions or tigers.
The best leaper, believe it or not, is not one of the top few largest. It’s the snow leopard. They are very powerful and will even run down a steep mountain chasing prey. They can jump 20 feet (six meters) vertically!
The best swimmer is the tiger, which very much loves water. Jaguars are very good swimmers also.
Most dangerous to humans
Some big cats almost never attack humans, or it’s incredibly rare. This includes jaguars, cheetahs, snow leopards, and some others large enough to kill humans if they choose to.
Of the ones that attack humans occasionally, the one that does it far more than any other is the leopard. Leopards hunt at night, see six times better in the dark than humans, are considered the most intelligent of all cats, some are black in color, they move silently, they are fearless about entering human habitations, and they are fast and powerful. Some decide they prefer to hunt humans, and individual leopards have killed over 100 people before being stopped.
Once there was a cat species larger than tigers
Smilodon was a resident of South America until goin extinct about 9,000 to 10,000 years ago. This species was larger than modern Bengal tigers. 
The saber-toothed cats, which famously went extinct by about 9,000 to 10,000 years ago, were not all true cats. However, some were. Of those that were truly part of the cat family, the largest was Smilodon. Smilodon lived in the Americas, and scientists believe it was slightly larger than the largest subspecies of tiger, which is the Bengal tiger. 
#1 - Tiger
Males of Bengal subspecies average 400 to 570 lbs
Bengal tigers in a national park in India.
#2 - Lion
Males in Southern Africa average 420 lbs
Male lion in Namibia, Southern Africa.
#3 - Jaguar
Males in Brazil and Venezuela average 220 lbs
Jaguars are stockier and thicker than leopards, and the spots are usually larger, with some appearing to have smaller spots within them.
#4 - Mountain lion
Males average 137 lbs
Mountain lions, or cougars, are the second-largest cat species in the Americas after jaguars.
#5 - Leopard
Males of the largest subspecies average 124 lbs
This is a Sri Lankan leopard, which is the largest of nine subspecies.
#6 - Cheetah
Males average 115 to 120 lbs
Cheetahs are well known as the world's fastest land animal, being able to top 70 mph (113 km per hour) in short bursts when hunting.
#7 - Snow leopard
Males average about 100 lbs
This photo of a snow leopard is from the San Diego Zoo in California, USA.
#8 - Eurasian lynx
Males average 40 to 66 lbs
Eurasian lynx in the snow in Germany.
#9 - Sunda clouded leopard
Adults weigh 26 to 55 lbs
This photo of a Sunda clouded leopard was taken on the island of Borneo.
#10 - Clouded leopard
Adults weigh 25 to 51 lbs
Photo of a clouded leopard taken in India, near the Myanmar border.