Reference Sheet

Geometry Reference Sheet

A quick visual-style guide for common geometry formulas, angle facts, coordinate geometry, and shape vocabulary.

Formula Sheet Scientific Calculator Unit Converter
Look for the shape, then choose area, perimeter, surface area, or volume.

∠Angles & Lines

Triangle angle sum
angle 1 + angle 2 + angle 3 = 180°All triangles have interior angles totaling 180 degrees.
Straight line
straight angle = 180°Angles that form a straight line add to 180°.
Full turn
circle angle = 360°A full rotation is 360 degrees.
Complementary angles
sum = 90°Two angles that add to a right angle.
Supplementary angles
sum = 180°Two angles that add to a straight line.

△Triangles

Triangle area
A = ½bhb is base; h is height.
Triangle perimeter
P = a + b + cAdd all side lengths.
Pythagorean theorem
a² + b² = c²For right triangles only. c is the hypotenuse.
Equilateral triangle
all sides equalAll angles are 60°.

□Quadrilaterals

Rectangle area
A = l × wLength times width.
Rectangle perimeter
P = 2l + 2wAdd all sides or double length and width.
Square area
A = s²s is the side length.
Parallelogram area
A = bhBase times height.
Trapezoid area
A = ½(b₁ + b₂)hAdd the bases, multiply by height, then divide by 2.

○Circles

Diameter
d = 2rDiameter is twice the radius.
Radius
r = d ÷ 2Radius is half the diameter.
Circumference
C = 2πr or C = πdDistance around a circle.
Circle area
A = πr²Square the radius, then multiply by pi.

▣3D Solids

Rectangular prism volume
V = l × w × hLength times width times height.
Cube volume
V = s³s is the side length.
Cylinder volume
V = πr²hArea of the circular base times height.
Cone volume
V = ⅓πr²hOne third of a cylinder with the same base and height.
Sphere volume
V = ⁴⁄₃πr³r is radius.

↗Coordinate Geometry

Slope
m = (y₂ − y₁) ÷ (x₂ − x₁)Rise over run.
Distance
d = √((x₂ − x₁)² + (y₂ − y₁)²)Distance between two points.
Midpoint
((x₁ + x₂) ÷ 2, (y₁ + y₂) ÷ 2)The point halfway between two points.
Ordered pair
(x, y)x moves left/right; y moves up/down.
Geometry problems often require a diagram, the correct formula, matching units, and careful checking of whether the answer should be length, area, or volume.