The formula is 4s{\displaystyle 4s}, where s{\displaystyle s} equals the side length of the square.A square has four equal sides, so you only need to know the length of one side to find the perimeter. 


, This information should be given, or you should be able to measure the side. If you do not know the length of the side, you cannot use this method.

For example, the perimeter of a square with a side length of  cm is shown by 4(4){\displaystyle 4(4)}.
 To do this, multiply the side length by 4. 

For example, 4×4=16{\displaystyle 4\times 4=16}. So the perimeter of the square is 16 cm.
 The formula is C=2π(r){\displaystyle C=2\pi (r)}, where C{\displaystyle C} equals the circumference of the circle and r{\displaystyle r} equals the length of the radius.The radius is the measurement between a circle’s center and edge., You are substituting the perimeter for C{\displaystyle C}, since the perimeter of the circle and the circumference of the circle are supposed to be equal.

For example, 16=2π(r){\displaystyle 16=2\pi (r)}.
 To do this, divide each side by 2π{\displaystyle 2\pi }. If you are not using a calculator, substitute 3.14 for the value of π{\displaystyle \pi }. This will give you the radius of the circle.

For example:16=2π(r){\displaystyle 16=2\pi (r)}162π=2π(r)2π{\displaystyle {\frac {16}{2\pi }}={\frac {2\pi (r)}{2\pi }}}166.28=6.28r6.28π{\displaystyle {\frac {16}{6.28}}={\frac {6.28r}{6.28\pi }}}2.55=r{\displaystyle 2.55=r}So the perimeter of a square with a side length of of 4cm is equal to the circumference of a circle with a radius of 2.55cm.
Set up the formula for the perimeter of a square.
 Plug the value of s{\displaystyle s} into the formula.
 Find the perimeter of the square.
 Set up the formula for the perimeter, or circumference, of a circle.
 Plug the perimeter of the square into the formula.
Solve for r{\displaystyle r}.
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