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Arc Length Calculator

Simply add the required values into this calculator to find the arc length of a curve, central angle, diameter, and more!

degrees (deg)

radians (rad)

gradians (gon)

(tr)

arcminute (arcmin)

Arc Second (arcsec)

milliradians (mrad)

microradians (μrad)

* π rad (pirad)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

nautical miles (nmi)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

nautical miles (nmi)

square millimeters (mm²)

square centimeters (cm²)

square decimeters (dm²)

square meters (m²)

square kilometers (km²)

square inchs (in²)

square feets (ft²)

square yards (yd²)

square miles (mi²)

are (a)

dalton (da)

hectare (ha)

(ac)

soccer fields (s_f)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

nautical miles (nmi)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

inches (in)

feets (ft)

yards (yd)

miles (mi)

nautical miles (nmi)

arc length img
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“Arc Length Calculator”

When any two of the following values are known, you can use the arc length calculator to find the length of an arc and other related measurements:

  • Sector Area
  • Chord Length
  • Radius of the Circle

Arc length is the distance along the curved line forming part of a circle between two points. Calculating the length of an irregular curve is called the rectification of a curve.

Arc Length Formula

For a circle, if the central angle is \(\theta = 360^\circ\) or \(2\pi\) radians, the arc length equals the circumference:

\(C = 2\pi r\)

For a central angle \(\theta\) in radians, the proportional relationship is:

\(\frac{L}{\theta} = \frac{C}{2\pi} = r \quad \Rightarrow \quad L = r \cdot \theta\)

⚠️ Note: Ensure \(\theta\) is in radians. If the angle is in degrees, convert first:

\(\theta_\text{radians} = \theta_\text{degrees} \times \frac{\pi}{180}\)

How to Calculate Arc Length

There are two common methods:

1. Using Radians:
\( s = r \cdot \theta \), where \(r\) is the radius and \(\theta\) is in radians.
2. Using Degrees:
\( s = 2 \pi r \cdot \frac{\theta}{360^\circ} \)

You can also use an arc length calculator for quick results.

Example 1:

Find the arc length and sector area for a circle with:

  • Radius: \( r = 50 \, \text{cm} \)
  • Central Angle: \( \theta = \frac{\pi}{4} \, \text{radians} \)

Solution:

Step 1: Arc Length

\( s = r \cdot \theta = 50 \cdot \frac{\pi}{4} = \frac{50\pi}{4} = \frac{25\pi}{2} \approx 39.27 \, \text{cm} \)

Step 2: Sector Area

\( A = \frac{1}{2} r^2 \theta = \frac{1}{2} \cdot 50^2 \cdot \frac{\pi}{4} = \frac{1250 \pi}{4} \approx 981.75 \, \text{cm}^2 \)

Arc Length Using Sector Area and Central Angle

If the sector area \(A\) and central angle \(\theta\) (in radians) are known:

\( L = \theta \cdot \sqrt{\frac{2A}{\theta}} \)

⚠️ Note: Convert \(\theta\) to radians if given in degrees.

Example 2:

Sector area: \( A = 300{,}000 \, \text{cm}^2 \), central angle: \( 60^\circ \). Find the arc length.

Solution:

Step 1: Convert area to square meters:

\( 300{,}000 \, \text{cm}^2 = 300{,}000 / 10{,}000 = 30 \, \text{m}^2 \)

Step 2: Convert angle to radians:

\( 60^\circ = 60 \cdot \frac{\pi}{180} = 1.0472 \, \text{radians} \)

Step 3: Apply the formula:

\( L = \theta \cdot \sqrt{\frac{2A}{\theta}} = 1.0472 \cdot \sqrt{\frac{2 \cdot 30}{1.0472}} \)

\( L = 1.0472 \cdot \sqrt{57.295} = 1.0472 \cdot 7.569 \approx 7.926 \, \text{m} \)

FAQ

Is Arc Length the Same as the Angle?

No, the angle measures the span between two radii, while the arc length is the distance along the circle between the two points.

What is the Difference Between Chord Length and Arc Length?

The chord length is the straight line connecting two points on a circle, whereas the arc length is the curved distance along the circle between the same points.

References

Wikipedia: Arc Length

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