.circle-calc-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e1e4e8;
border-radius: 12px;
background-color: #ffffff;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
color: #333;
}
.circle-calc-header {
text-align: center;
margin-bottom: 30px;
}
.circle-calc-form {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
margin-bottom: 25px;
}
.circle-input-group {
display: flex;
flex-direction: column;
}
.circle-input-group label {
font-weight: 600;
margin-bottom: 8px;
font-size: 14px;
color: #444;
}
.circle-input-group input, .circle-input-group select {
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 16px;
}
.circle-calc-btn {
grid-column: span 2;
background-color: #2c3e50;
color: white;
padding: 15px;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.2s;
}
.circle-calc-btn:hover {
background-color: #34495e;
}
.circle-result-box {
background-color: #f8f9fa;
padding: 20px;
border-radius: 8px;
text-align: center;
margin-top: 20px;
border: 1px solid #eaeeef;
}
.circle-result-value {
font-size: 28px;
font-weight: 800;
color: #27ae60;
margin-top: 10px;
}
.circle-article {
margin-top: 40px;
line-height: 1.6;
color: #444;
}
.circle-article h2 {
color: #2c3e50;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
margin-top: 30px;
}
.circle-article p {
margin-bottom: 15px;
}
.circle-formula {
background: #eee;
padding: 15px;
font-family: "Courier New", Courier, monospace;
display: block;
text-align: center;
margin: 20px 0;
font-weight: bold;
border-radius: 4px;
}
@media (max-width: 600px) {
.circle-calc-form {
grid-template-columns: 1fr;
}
.circle-calc-btn {
grid-column: span 1;
}
}
How to Calculate the Area of a Circle
The area of a circle represents the total space contained within the boundary of its perimeter. In geometry, the area is calculated using the distance from the center to the edge (the radius).
Area = π × r²
Where:
- π (Pi): Approximately 3.14159
- r: The radius of the circle
Using the Radius vs. Diameter
The radius is exactly half of the diameter. If you only know the diameter of a circle, you can find the area by either dividing the diameter by two to find the radius first, or by using the specific diameter formula:
Area = (π / 4) × d²
Step-by-Step Example
Let's say you have a circular table with a radius of 5 feet. To find the area:
- Square the radius: 5 × 5 = 25
- Multiply by Pi (3.14159): 25 × 3.14159 = 78.53975
- Result: The area is approximately 78.54 square feet.
Why Use This Calculator?
Whether you are calculating the amount of fabric needed for a circular tablecloth, the amount of mulch for a garden bed, or solving a complex engineering problem, precision is key. Our circle area calculator uses the high-precision value of Pi provided by modern JavaScript engines to ensure your math is perfect every time.
function updateLabels() {
var type = document.getElementById('inputType').value;
var label = document.getElementById('dimensionLabel');
if (type === 'radius') {
label.innerText = 'Radius Value:';
} else {
label.innerText = 'Diameter Value:';
}
}
function calculateCircleArea() {
var val = parseFloat(document.getElementById('circleValue').value);
var type = document.getElementById('inputType').value;
var unit = document.getElementById('unit').value;
var areaOutput = document.getElementById('areaOutput');
var circumferenceOutput = document.getElementById('circumferenceOutput');
var resultDisplay = document.getElementById('resultDisplay');
if (isNaN(val) || val <= 0) {
alert("Please enter a valid positive number.");
return;
}
var radius;
if (type === 'radius') {
radius = val;
} else {
radius = val / 2;
}
var area = Math.PI * Math.pow(radius, 2);
var circumference = 2 * Math.PI * radius;
areaOutput.innerHTML = area.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 4}) + " " + unit + "²";
circumferenceOutput.innerHTML = "Circumference: " + circumference.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 4}) + " " + unit;
resultDisplay.style.display = 'block';
}