Download Calculating Surface Area Instructions

Calculating Area, Surface Area and Perimeter Instructions:
Area of a rectangle: length x width (squared units)
Area of a triangle: base x height, divided by 2 (or base x height x ½) (squared units)
Perimeter of any figure: Add up the lengths of all sides on the outside of the figure. If it is not already
there, figure it out from the other sides that are there. (“plain” units because it is length.) Must add ALL
sides!
Area of Compound Figure: (#1 and #2)
1. Break the compound figure into smaller sections of figures you know (rectangles and/or
triangles)
2. Find the area of each section (lw for rectangles or lw divided by 2 for triangles)
3. Add the areas of each section together.
4. Answer in squared units (because it is area)
Surface are of a rectangular PRISM: (# 3and #4)
1.
2.
3.
4.
5.
6.
2(lw + lh + wh) or 2lw+2lh+2wh
First multiply the length times the width
Then multiply the length times the height
Then multiply the width times the heigh
Add all of these numbers together and multiply by 2 (because there are 2 of each face)
Answer in squared units (because it is area.)
___________________________________________OR______________________________________
2 times the length times the width
plus
2 times the length times the height
plus
2 times the width times the height
Answer in squared units (because it is area)
Surface Area of a triangular PYRAMID (#6)
B + area of all side triangles (B = area of base)
1. Find the area of the base (if it’s a rectangular prism, multiply the length of the base of the
rectangle times the length of the width of the rectangle.)
2.
3.
4.
5.
6.
Put this number aside and label it “area of base”
Multiply the base of the triangle times the height of the triangle and divide by 2
Multiply this number by 4 (because there are 4 triangles that have the same area)
Add this number to the “area of the base” that you found before.
Answer in squared units (because it is still area if it’s surface area.)
Surface area of a triangular prism (#7 and 8)
1. Find the area of 1 triangle (bh divided by 2)
2. Multiply this by 2 (because there are 2 congruent, parallel bases that are triangles)
3. Put this number aside and label it “area of both triangular bases”
Be sure you remember that the rectangular sides are not necessarily the same (congruent) so
you can’t just find 1 and multiply that by 3!
4. Find the area of 1 of the rectangular sides (lw)
5. Find the area of another of the rectangular sides (lw)
6. Find the area of the last rectangular side (wh)
Add the “area of both triangles” to the area of all 3 of the “rectangular sides”
Answer in squared units (because it is area)
Figuring out whether you are finding surface area or volume in a word problem: (#9)
If you are trying to find out how much is on the outside of a figure, you are looking for surface area
(because the surface is the outside of the figure.)
If you are trying to find out how much is inside the figure, you are looking for volume.
Pyramids have 1 base and trianglular sides
Prisms have 2 congruent, parallel bases and rectangular sides