# Semicircle Area Calculator

With this semicircle area calculator, you can quickly **find the area of half of a circle** 🌗. What is more, the tool also doubles as a **semicircle perimeter calculator**, so inputting radius or diameter will help you find the basic features of the shape in the blink of an eye. In the article below, we provide the **semicircle definition** and explain how to find the perimeter and area of a semicircle. So what are you waiting for? Scroll down!

However, if you're searching for a moment of inertia of a semicircle, check out our comprehensive moment of inertia calculator.

## What is a semicircle?

A semicircle is simply **half of a circle**. You'll get a semicircle when you cut a circle along a diameter line — or, in other words, through the circle center. The prefix *semi-* comes from Latin, meaning half or partly (like in words such as semi-permanent, semi-formal, and semifinal).

💡 Once know the etymology, you won't forget what a semicircle is: just remind yourself how the semifinals are connected with the finals, and you'll know how to link a semicircle to a circle!

## How to find the area of a semicircle? Semicircle area formula

Knowing the semicircle definition – half of a circle – we can easily write the semicircle area formula using the well-known circle area, $\pi\cdot r^2$:

The area of a semicircle is just half of the area of a full circle. But can we use this rule for the circumference of a semicircle?

## Perimeter of a semicircle formula (aka circumference of a semicircle)

If you want to calculate the outer boundary of a semicircle – the circumference or perimeter of a semicircle – you need to be careful not to fall into any traps. **The circumference of a semicircle is not equal to half of the circle circumference** - you need to add also the diameter of the semicircle, as another boundary was created:

Then:

Or:

Where $d$ is the semicircle diameter

## Find the area of a half circle with semicircle area calculator

Where do we find semicircular objects in everyday life? The shape of a half circle occurs in:

**Home furniture and decorations**such as mirrors, tables with semicircular counters, sofas, benches, rugs, or even windows.**Everyday objects**like fans, protractors, circle skirts.**All food that comes in round, cylindrical, or sphere shapes**could also be sliced to approximate semicircles. For example, half a pizza, a slice of watermelon 🍉 or half a cookie 🍪

Let's figure out how to find an area of a semicircular object – a rug that would fit perfectly in front of your fireplace🔥:

**Input the diameter or radius of the rug.**Assume that our fireplace is $4\ \mathrm{ft}$ wide, so we'd like to have the same rug length. Enter $4\ \mathrm{ft}$ in the diameter box. Change the length units by clicking on the unit name and selecting the one you need from the drop-down list.- The
**semicircle area calculator displays the area of half-circle**: for our rug, it's $6.28\ \mathrm{ft^2}$. - The tool works as
**semicircle perimeter calculator**as well – e.g., if you want to braid the rug, you can calculate how much lace you'll need. In our case, the perimeter equals $10.28\ \mathrm{ft}$.

Now, as you know everything about semicircles, maybe you'd like to check our other circle-related calculators 🔴?

## FAQ

### How do I find the perimeter of a semicircle given radius?

To determine the perimeter of a semicircle:

- Write down the
**radius**`r`

. **Multiply**the radius by`π+2`

:`r × (π+2) ≈ 5.14159 × r`

.- The result is the
**perimeter of your semicircle**. You can verify the result with our online semicircle perimeter calculator.

### Is the semicircle perimeter half of circle perimeter?

**No**, the circumference of a semicircle is **greater than** half of the circle circumference. This is because the "flat" side of the semicircle also contributes to the perimeter. It is equal to the (semi)circle's diameter. Thus, `semicircle perimeter = half of circle's perimeter + circle's diameter`

.

### What is the area of a semicircle with radius 10 in?

The area is **157.08 in sq**. To arrive at this answer, recall that the area of a semicircle is half the area of the circle. That is, the semicircle area formula reads `Area = πr²/2`

. Plugging in `r = 10 [in]`

, we get `100π / 2 [in sq] ≈ 157.08 [in sq]`

. Don't hesitate use our online semicircle area calculation if you struggle with the calculations.