Plane area and perimeter formulas
Area measures covered surface; perimeter measures boundary length.
Key knowledge
In Euclidean geometry, rectangle area is length times width, triangle area is half base times perpendicular height, and circle area is π times radius squared. Circle circumference is 2π times radius.
Values and equations
A_rectangle=LW; A_triangle=bh/2; A_circle=πr^2; C_circle=2πr
- L, W
- Rectangle side lengths length
- b, h
- Triangle base and perpendicular height length
- r
- Circle radius length
- A_rectangle, A_triangle, A_circle
- Areas length²
- C_circle
- Circle boundary length length
- π
- Circle constant dimensionless
Conditions and scope
- Use nondegenerate shapes, positive lengths and one common length unit.
- The triangle's height is perpendicular to the line containing its base; area has square units and perimeter has length units.
Euclidean plane formulas only. π kept exact; source's suggested decimal substitutions are not definitions.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Lynn Marecek, MaryAnne Anthony-Smith and Andrea Honeycutt Mathis / OpenStax2 sources
Evidence and review
Checked the stated plane area and perimeter formulas and restrictions against the listed primary sections; exact inspected boundaries are in the author receipt.
2026-10-10 · Independent Physics and Measurement reference editor (AI editorial bounded review). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
Permanent link to this entry ↗- Record identity
- foundation-math-plane-areas
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions