# Billion

A billion is a number that is represented as 1,000,000,000, or 10^{9}, or in scientific notation, 1 × 10^{9}. It can also be defined as one thousand million (1,000 × 1,000,000).

### How big is a billion?

Although the definition of a billion is fairly straightforward, it is such a large number that it may be hard to conceptualize how much a billion actually represents. Relating it to things people do every day can help make it easier to grasp.

Example

Let's say that on average, you walk 1 kilometer per day. 1 kilometer = 1,000 meters. How many days would it take for you to walk 1 billion meters?

1,000,000,000 meters ÷ 1,000 meters/day = 1,000,000 days

So if you walk 1 kilometer per day, it will take you 1 million days to walk 1 billion meters. 1 million is still a large number and may still be difficult to conceptualize, so let's take it further.

1 million days is equivalent to approximately 2,740 years. This is far longer than any human can live, so it is impossible for us to walk 1 billion meters if we walk an average of 1 kilometer per day. How many kilometers would we have to walk in a day on average to be able to walk 1 billion meters in an average human lifespan?

Let's assume a lifespan of 80 years, and that we start walking at the age of two. This gives us 78 years, or 28,470 days, to walk 1 billion meters.

1,000,000,000 meters ÷ 28,470 days = 35,124 meters/day

So we would have to walk about 35 kilometers or 21 miles per day from the time we begin walking, up until death, to be able to walk 1 billion meters in an 80 year lifespan.

A full marathon is 42.195 kilometers, or 26.2 miles. A marathon is something that many people never run, or even walk once in their lifetime (in a day), so a billion is such a large number that virtually nobody will ever travel the distance of 1 billion meters on foot in their lifetime!