How to Solve Geometry Calculations

Use formulas to determine the perimeter, area and volume of geometrical figures.
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Geometry calculations often involve determining the perimeter and area of polygons and the volume of solid figures. Perimeter measures the length around a flat shape while area measures the surface of the shape. Volume measures the capacity of a solid figure. To solve geometry calculations, use formulas when measuring perimeter, area and volume.


    Determine the formula or method needed to find the perimeter of the polygon you are measuring. Use the formula P = 4_s (perimeter = four times the length of one side) to find the perimeter of a square. To find the perimeter of a rectangle use the formula P = 2_l + 2*w (perimeter = two times the length plus two times the width). To find the perimeter of other polygons, simply add up the sides.

    Replace the variables with numbers. Use a ruler to determine the value of each side of the polygon. If the measurements are provided for you, simply insert the correct numbers into the formula.

    Solve the formula to determine perimeter. When using the formula for a rectangle, remember to multiply the length times two and the width times two and then add the two products together.


    Determine if the figure is a triangle, square, rectangle or parallelogram. A triangle has three sides, and polygons have four sides. Both squares and rectangles have four right angles. However, a square has four equal sides while a rectangle has only two equal sides. A parallelogram has two sets of parallel sides, but the angles do not measure 90 degrees.

    Select the correct area formula for the polygon you are measuring. Use A = ½(b)_h/2 (area = one half base times height or base times height divided by two) to determine the area of a triangle. To find the area of a square, use A = s_s (area = side times side). Find the area of a rectangle using the formula A = l_w (area = length times width). The area of a parallelogram can be found using the formula A = b_h (area = base times height).

    Solve the formula to determine the area. Replace the variables with values for the base, height, length and width, and complete the equation.


    Determine the length, width and height of the solid figure. Use a ruler to measure each, and determine the value.

    Enter the values for each into the formula V = l_w_h (volume = length times width times height). First enter the value for length, then the value for width and then the value for height.

    Solve the equation to determine volume. First multiply the length by the width. Then multiply the product of those two by the height.


    • Remember to include the unit of measure in your answer. Also remember that the answer for area will be noted in units squared.

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