Geometry
29 free online calculators — instant results, no sign-up
All 29 Geometry Tools
Pentagram Area Calculator
golden ratio & shoelace exactCircle Intersection Calculator
overlap area & common chordCircle Calculator
Area, circumference, diameter and arc lengthTriangle Calculator
Area, perimeter, angles and heightRectangle Calculator
Area, perimeter and diagonalSphere Calculator
Volume, surface area and diameterTrapezoid Calculator
Area, perimeter and medianNEWCone Calculator
Volume, lateral area and slant heightNEWCylinder Calculator
Volume, lateral and total surface areaNEWEllipse Calculator
Area and circumference approximationNEWParallelogram Calculator
Area, perimeter and heightRegular Polygon Calculator
Area, perimeter, angles, circumradius and inradiusPythagorean Theorem Calculator
Find the third side of a right triangleSector Calculator
Arc length, area, chord and segment from radius and angleCuboid Calculator
Volume, surface area, space diagonal and edge sumPyramid Calculator
Square pyramid volume, lateral area and slant heightFrustum Volume Calculator
Truncated cone volume, slant height and surface areaEllipsoid Volume Calculator
Ellipsoid volume and Knud Thomsen surface areaAnnulus Calculator
Ring area π(R²−r²), width and circumferencesCircular Segment Calculator
Area, arc length, chord from any two valuesTube & Pipe Calculator
Hollow cylinder weight, volume, surface areaPolygon Area Calculator
Shoelace formula from vertex coordinates, centroidTorus Calculator
V=2π²Rr², surface areaSpherical Cap Calculator
Volume, cap area, dome headsRhombus & Kite Calculator
Diagonal area, sides & anglesGolden Ratio Calculator
0.618 split, golden rectangle, FibonacciRegular Hexagon Calculator
Side, across-flats, area · nut wrench sizesSpecial Right Triangle Calculator
30-60-90 and 45-45-90, one side fixes allMidpoint Calculator
Midpoint of two points, endpoint back-solve, distanceRelated Guides
Circle: Circumference & Area Formulas with Examples
C = 2πr = πd; A = πr². r=5 → C = 31.4, A = 78.5. Remember: area uses the radius SQUARED — doubling r quadruples the area. Includes arc/sector formulas, π approximations and worked pizza-size math.
Triangle Area: The 4 Formulas & When to Use Each
Base-height: A = bh/2. Three sides: Heron's formula √[s(s−a)(s−b)(s−c)]. Two sides + included angle: A = ½ab·sinC. Right triangle: A = ½ × legs. Includes the triangle inequality check and worked examples for each.
Rectangle & Square: Area, Perimeter & Diagonal
Rectangle: A = l×w, P = 2(l+w), diagonal = √(l²+w²). Square: A = s², P = 4s, diagonal = s√2. 5×3 rectangle → A = 15, P = 16, d = 5.83. Includes unit conversion traps and flooring/fencing worked examples.
Sphere: Surface Area & Volume Formulas Explained
Surface area = 4πr²; volume = (4/3)πr³. r = 3: SA = 113.1, V = 113.1 (numerically equal only at r=3). Doubling radius → 8× volume. Includes hemisphere formulas, the Archimedes cylinder relation, and ball-tank math.
Trapezoid Area: Formula, Midline & Examples
A = (a + b) × h ÷ 2 — average of the parallel sides times height. a=8, b=5, h=4 → A = 26. The midline (median) = (a+b)/2, so area = midline × height. Includes height-finding, isosceles diagonals, and the parallelogram connection.
Cone: Volume & Surface Area Formulas with Examples
V = (1/3)πr²h — exactly one third of the matching cylinder. Lateral area = πrl where slant l = √(r²+h²); total = πr(r+l). r=3, h=4 → l=5, V = 37.7, total SA = 75.4. Includes the 3-4-5 classic and ice-cream-cone math.