Content

• Steps
• Method 1 of 4: Standard Method
• Method 2 of 4: Calculate the perimeter through the area and one side
• Method 3 of 4: Perimeter of a rectangular shape
• Method 4 of 4: Perimeter of a rectangular shape (only some sides are known)
• What do you need
• Additional articles

Calculating the perimeter of a rectangle is a fairly straightforward task. All you need to know is the width and length of the rectangle. If these values ​​are not given, you need to find them. This article will show you how to do this.

Steps

Method 1 of 4: Standard Method

1. 1 Formula for calculating the perimeter. Basic formula for calculating the perimeter of a rectangle: P = 2 * (l + w).
   • Remember: the perimeter is the total length of all sides of the shape.
   • In this formula P - "perimeter", l - the length of the rectangle, w - the width of the rectangle.
   • The length always has a greater value than the width.
   • Since the rectangle has two equal lengths and two equal widths, only one side is measured l (length) and one side w (width) (although the rectangle has four sides).
   • You can also write the formula as: P = l + l + w + w
2. 2 Find the length and width. In a common math problem, the length and width of a rectangle are usually given. If you are looking for the perimeter of a rectangle in real life, use a ruler or tape measure to find the length and width.
   • If you are calculating the perimeter of a rectangle in real life, use a tape measure or measuring tape to find the length and width of the area you want. If you are working outdoors, measure all sides to make sure the parallel sides really match.
   • For example: l = 14 cm, w = 8 cm
3. 3 Add up the length and width. Plug the values ​​into the formula and add them up.
   • Note that according to the order of operations, the mathematical expressions in parentheses are solved first.
   • For example: P = 2 * (l + w) = 2 * (14 + 8) = 2 * (22)
4. 4 Multiply this amount by two (according to the formula).
   • Note that by multiplying the sum by two, you have included the other two sides of the rectangle. By folding the width and length, you are only folding the two sides of the shape. Since the other two sides of the rectangle are equal to two folded ones, the sum is simply multiplied by two and thus the total of all four sides is found.
   • The resulting number will be the perimeter of the rectangle.
   • For example: P = 2 * (l + w) = 2 * (14 + 8) = 2 * (22) = 44 cm
5. 5 Alternative method: fold l + l + w + w... Instead of adding two sides and multiplying them by two, you can simply add all four sides and find the perimeter of the rectangle.
   • If the concept of perimeter is difficult for you, then this method is just for you.
   • For example: P = l + l + w + w = ​​14 + 14 + 8 + 8 = 44 cm

Method 2 of 4: Calculate the perimeter through the area and one side

1. 1 Formula for the area of ​​a rectangle. If you are given the area of ​​a rectangle, you must know the formula for calculating it in order to find the missing information to calculate the perimeter.
   • Remember: the area of ​​a shape is the value of the total space, which is limited by the sides of the shape.
   • Formula for calculating the area of ​​a rectangle: A = l * w
   • Formula for calculating the perimeter of a rectangle: P = 2 * (l + w)
   • In the above formulas BUT - "square", P - "perimeter",l - the length of the rectangle, w - the width of the rectangle.
2. 2 Divide the area by the side given in the problem to find the other side.
   • Since to calculate the area you need to multiply the length by the width, then dividing the area by the width, you get the length. Likewise, dividing area by length will give you width.
   • For example: A = 112 cm2, l = 14 cm
     • A = l * w
     • 112 = 14 * w
     • 112/14 = w
     • 8 = w
3. 3 Add length and width. Now that you have the length and width values, you can plug them into the formula to calculate the perimeter of the rectangle.
   • The first step is to add the length and width, since this part of the equation is in parentheses.
   • According to the order of evaluation, the action in parentheses is performed first.
4. 4 Multiply the sum of the length and width by two. After you have added the length and width of the rectangle, you can find the perimeter by multiplying that number by two. This is necessary to add the remaining two sides of the rectangle.
   • The opposite sides of the rectangle are equal, which is why the sum of the length and width must be multiplied by two.
   • Both the length of the opposite sides and the width are the same.
   • For example: P = 2 * (14 + 8) = 2 * (22) = 44 cm

Method 3 of 4: Perimeter of a rectangular shape

1. 1 Write down the basic formula for determining the perimeter. Perimeter is the total length of all sides of the shape.
   • The rectangle has four sides. The sides making up the length are equal to each other and the sides making up the width are equal to each other. Thus, the perimeter is the sum of these four sides.
   • Rectangular shape. Consider an "L" shape. Such a shape can be split into two rectangles. However, when calculating the perimeter of a shape, such a division into two rectangles is not taken into account. The perimeter of the figure in question: P = S1 + S2 + S3 + S4 + S5 + S6, where S are the sides of the figure (see figure).
   • Each “s” is a separate side of a compound rectangle.
2. 2 In a common math problem, the sides of a figure are usually given. If you are looking for the perimeter of a rectangular shape in real life, use a ruler or tape measure to find the sides.
   • For explanation, we introduce the following notation: L, W, l1, l2, w1, w2... Uppercase L and W indicate the full length and width of the figure. Lowercase l and w indicate the partial length and width of the figure.
   • Thus, the formula P = S1 + S2 + S3 + S4 + S5 + S6 is written as: P = L + W + l1 + l2 + w1 + w2 (both formulas are essentially the same, but use different variables).
   • Variables "w" and "l" are just substitutes for numbers.
   • Example: L = 14 cm, W = 10 cm, l1 = 5 cm, l2 = 9 cm, w1 = 4 cm, w2 = 6 cm.
     • note that l1+l2=L... Similarly, w 1+ w2=W.
3. 3 Fold the sides. Plug the values ​​into the formula and calculate the perimeter of the rectangular shape.
   • P = L + W + l1 + l2 + w1 + w2 = 14 + 10 + 5 + 9 + 4 + 6 = 48 cm

Method 4 of 4: Perimeter of a rectangular shape (only some sides are known)

1. 1 Analyze the side values ​​given to you. You can find the perimeter of a rectangular shape if you are given at least one full length or full width and at least three partial widths and lengths.
   • For an "L" -shaped rectangular shape, use the formula P = L + W + l1 + l2 + w1 + w2
   • In the above formula: P Is the perimeter, uppercase L and W indicate the full length and width of the figure. Lowercase l and w indicate the partial length and width of the figure.
   • Example: L = 14 cm, l1 = 5 cm, w1 = 4 cm, w2 = 6 cm; It is required to find: W, l2.
2. 2 Find the unknown sides using the given side values. Please note that l1+l2=L... Similarly, w 1+ w2=W.
   • For example: L = l1 + l2; W = w1 + w2
     • L = l1 + l2
     • 14 = 5 + l2
     • 14 - 5 = l2
     • 9 = l2
     • W = w1 + w2
     • W = 4 + 6
     • W = 10
3. 3 Fold the sides. Plug the values ​​into the formula and calculate the perimeter of the rectangular shape.
   • P = L + W + l1 + l2 + w1 + w2 = 14 + 10 + 5 + 9 + 4 + 6 = 48 cm

What do you need

• Pencil
• Paper
• Calculator (optional)
• Ruler or tape measure (optional)

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