Math & Scientific tool map
Geometry
Shapes, angles, coordinates, area, and volume.
Choose the tool whose inputs and output match your task. Check each calculator’s assumptions and limitations before using its result.
Latest update:
Circle geometry shows up wherever you measure round things: a pizza pan by radius, a pipe by circumference, a garden bed by diameter. The circle calculator starts from any one positive measurement and returns radius, diameter, circumference, and area in consistent units, so you never have to remember which formula converts between them. When trigonometry enters the picture, the half-angle calculator finds the sine, cosine, and tangent of half an angle, with quadrant-aware signs — useful for exact trig tables, integration substitutions, and geometry proofs. Start from the quantity you actually know, and check your units before entering values. More shape and angle tools live in the Math & Scientific collection.
2 of 2 calculators
Geometry2 calculators
Circle Calculator: Radius, Diameter, Circumference, Area
Find a circle's radius, diameter, circumference, and area from any one positive measurement, with formulas, unit rules, inverse cases, and checked arithmetic.
Updated
Verified
Half Angle Calculator
Calculate sine, cosine, and tangent of half an angle in degrees, with half-angle identities, quadrant signs, domain limits, and a checked example.
Updated
Verified
Circle Calculator: Radius, Diameter, Circumference, Area
Find a circle's radius, diameter, circumference, and area from any one positive measurement, with formulas, unit rules, inverse cases, and checked arithmetic.
Updated
Verified
Half Angle Calculator
Calculate sine, cosine, and tangent of half an angle in degrees, with half-angle identities, quadrant signs, domain limits, and a checked example.
Updated
Verified
Frequently asked questions
- What can the circle calculator solve from one value?
- It can start from radius, diameter, circumference, or area. Once one positive measurement is entered, the calculator converts it to radius first, then reports radius, diameter, circumference, and area rounded to four decimal places for consistent comparison across all four standard circle measurements.
- What units should I enter?
- Use one consistent length unit for radius, diameter, or circumference, such as inches, centimeters, meters, or feet. The returned area uses the square of that unit. If you enter area first, the value should already be in square units, such as square inches or square meters.
- Can a circle have a zero radius in this calculator?
- Mathematically, a radius of zero describes a degenerate circle with zero circumference and zero area. This calculator requires a value greater than zero, so it rejects zero and negative inputs rather than displaying a degenerate case or an impossible physical measurement.