If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains ***.kastatic.org** and ***.kasandbox.org** are unblocked.

Main content

Current time:0:00Total duration:3:21

CCSS.Math:

when people use the word perimeter in everyday language they're talking about the boundary of some area and when we talk about perimeter in math we're talking about a related idea but now we're not just talking about the boundary we're actually talking about the length of the boundary how far do you have to go around the boundary to essentially go completely around the figure completely go around the area so let's look at this first triangle right over here it has three sides that's why it's a triangle so what's its perimeter well here all the sides are the same so the perimeter for this triangle is going to be four plus four plus four and whatever units this is if this is four feet four feet and four feet there'd be four feet plus four feet plus four feet is equal to twelve feet now I encourage you to now pause the video and figure out the perimeters of these three figures well it's the exact same idea we would just add the lengths of the sides so let's say that these distances and their let's say they're in meters so let's say that this is three meters and this is also three meters as a rectangle here so this is five meters this is also five meters so what is the perimeter of this rectangle going to be what is the distance around the rectangle that bounds this area well it's going to be three plus five plus three plus five which is equal to let's see that's 3 plus 3 is 6 plus five plus five is ten so that is equal to 16 and if we're saying these are all in meters these are all in meters then it's going to be 16 meters now what about this Pentagon let's say that each of these sides are 2 and I'll make up I'll make up a unit here let's say there are two canoes two canoes that's a new unit that I have a new unit of distance that I have just that I have just invented 2 - good news - good news so what is the perimeter of this Pentagon in good news well it's 2 plus 2 plus 2 plus 2 plus 2 Guu or we're essentially taking one two three four five good news five five sides each have a length of two good news so the perimeter here we could add to repeatedly five times or you could just say this is five times two good news which is equal to ten good news we're going to is a completely made-up unit of length that I just made up here we have a more irregular polygon but same exact idea how would you figure out its perimeter well you just add up the lengths of its sides and here I'll just do it Union less I'll just assume that this is some generic units and here the perimeter will be one plus four plus two plus two let me scroll over to the right a little bit plus four plus six so what is this going to be equal to 1 plus 4 is 5 plus 2 is 7 plus 2 is 9 plus 4 is 13 plus 6 is 19 so this figure has a perimeter of 19 and whatever units these distances are actually given