Turn any circle measurement into exact area. Switch units instantly and keep your calculations organized. Download your table as CSV or a PDF report.
| Date/Time | Based On | Unit | π | Radius | Diameter | Circumference | Area |
|---|---|---|---|---|---|---|---|
| No saved results yet. Run a calculation to build your table. | |||||||
Sample radii and areas using π ≈ 3.14159 (centimeters).
| Radius (cm) | Diameter (cm) | Circumference (cm) | Area (cm²) |
|---|---|---|---|
| 2 | 4 | 12.56636 | 12.56636 |
| 5 | 10 | 31.41590 | 78.53975 |
| 7.5 | 15 | 47.12385 | 176.71459 |
| 10 | 20 | 62.83180 | 314.15900 |
If you enter diameter, the calculator first finds r = d ÷ 2. If you enter circumference, it first finds r = C ÷ (2π), then applies A = πr².
This calculator accepts radius, diameter, or circumference to derive a single consistent radius. If you enter diameter, it divides by 2; if you enter circumference, it divides by 2π. Using one source value reduces ambiguity, while optional extra fields enable quick validation. Example: C = 31.4159 cm implies r ≈ 5 cm.
Circle area grows with the square of radius, so doubling r multiplies area by 4. For example, r = 5 cm gives A ≈ 78.54 cm², while r = 10 cm gives A ≈ 314.16 cm². This quadratic behavior matters in design, machining, irrigation coverage, and packaging.
Linear units convert through a scale factor, but area converts through the square of that factor. Switching from centimeters to meters divides numeric area by 10,000 because (0.01 m)² = 0.0001 m². The calculator keeps outputs in the chosen unit and labels area using unit² for clarity. A 7.5 cm radius circle reports ≈ 176.71 cm², or ≈ 0.017671 m².
The π option affects rounding, especially for large circles. 22/7 is convenient for mental math, 3.14159 suits coursework, and high‑precision π helps when tolerance is tight. Decimal places allow consistent reporting; 2 decimals fits estimates, while 6–10 decimals supports detailed reports. Using 22/7 introduces about 0.04% relative error versus π; at r = 100 cm, that can shift area by roughly 12.7 cm².
When multiple inputs are provided, the tool compares them and warns if they disagree beyond a small threshold. This catches common mistakes such as mixing units, typing diameter as radius, or copying circumference from another problem. Only positive values are accepted to keep geometry physically meaningful. If your diameter is 20 cm, the radius should be 10 cm.
The history table stores up to 20 recent calculations per session, creating a small audit trail. CSV export supports spreadsheets for batch work, while PDF export produces a clean report containing the latest result plus the full table. This is useful for lessons, quotes, and project documentation. Keep unit and decimals consistent for easy, quick comparisons.
Enter the measurement you already know. Radius is simplest. Diameter and circumference work too, because the calculator converts them into radius before computing area.
Area measures surface, not length. When a circle uses centimeters, the area is in cm². Switching units changes the numeric value, but the physical area stays the same.
Use high‑precision π for engineering, 3.14159 for most learning tasks, and 22/7 for quick manual checks. The difference becomes more noticeable as the radius grows.
The calculator prioritizes radius, then diameter, then circumference. If the extra fields disagree beyond a small tolerance, you will see a warning so you can recheck entries and units.
The graph plots area A = πr² across a radius range using your current π selection and unit. If a result exists, it marks your computed point for visual comparison.
CSV downloads the history table for spreadsheet use. PDF generates a formatted report containing the latest result and the same table, which is convenient for sharing or printing.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.