How do you find semicircle area?
A = (1/2)πr².
Area of a Semicircle Calculator
Find the area of a half-disk from radius or diameter.
Enter radius or diameter
Choose input mode and provide a positive length.
About this calculator
How to use Area of a Semicircle Calculator, plus the formulas and logic behind the results.
Tool description
A semicircle area is half of πr². This is the region of the half-disk, not just the curved boundary.
How to use
- Select radius or diameter mode.
- Enter a positive length.
- Select Calculate.
- Review area and related full-circle area.
Formulas & reference
A = (1/2) π r²r = d/2
Semicircle notes
- Half of full circle area
- r = 2 → A = 2π
- Diameter mode sets r = d/2
- Positive length required
Calculation logic
Converts diameter to radius when needed, then applies half of πr² using M_PI.
Perimeter of a semicircle region would also include the diameter; this tool reports area only.
Area of a Semicircle Calculator FAQ
Common questions about this calculator and how to use the results.
Can I use diameter?
Yes. Convert with r = d/2 first (built into diameter mode).
Is the flat side included in area?
Area is the half-disk region enclosed by arc and diameter.
What about perimeter?
Perimeter = πr + d = πr + 2r; not computed here.
Is this a sector of 180°?
Yes—the area matches a 180° sector.
What π is used?
M_PI.