Geometry Calculators
Use the Day 9 geometry set to calculate area, perimeter, circle measurements, and triangle values. Each page starts with the live calculator and keeps formulas, FAQs, related links, and print controls below the fold.
Live today
4 calculators + 1 reference
Area, perimeter, circle, triangle, and the area formulas printable reference are now live with shape-specific formulas, unit notes, example checks, and printable result sections.
Day 9 geometry tools
Geometry Calculator
Area Calculator
Calculate rectangle, triangle, circle, and trapezoid area with unit conversions, copy controls, and printable formula support.
Open calculatorGeometry Calculator
Perimeter Calculator
Calculate square, rectangle, triangle, and circle perimeter or circumference with unit conversions and printable formula results.
Open calculatorGeometry Calculator
Circle Calculator
Calculate circle diameter, circumference, area, sector area, and arc length with length and area unit conversions.
Open calculatorGeometry Calculator
Triangle Calculator
Calculate triangle perimeter, semiperimeter, Heron area, base-height area, side validity, type, and unit conversions.
Open calculatorGeometry formulas covered in this release
Area formulas
Calculate surface coverage for rectangles, triangles, circles, and trapezoids.
Perimeter formulas
Measure outside-edge distance for polygons and circumference for circles.
Triangle and circle support
Check triangle validity and calculate circle sectors, arcs, diameter, and area.
How the Day 9 tools connect
Coverage versus edge length
Area answers how much surface a shape covers. Perimeter answers how far it is around the outside edge. The hub links those calculators together so users choose the correct unit type before copying the result.
Special shape checks
Circle and triangle pages add the extra context those shapes need: pi-based measurements, sector angle, arc length, triangle inequality, Heron's formula, and side classification.
Supporting Reference