ACT Math · Formula Sheet
ACT Math Geometry: Every Formula You Need + Free Practice Quizzes
Geometry is the single largest topic on the ACT Math section — about 12–15 questions per test. Unlike the SAT, the ACT does NOT provide a formula sheet. You must have the formulas memorized. This guide gives you every geometry formula tested on the ACT, organized by shape, plus links to 8 free practice quizzes to test your knowledge.
Triangle Formulas
Triangles
Area: A = ½ × base × height
Pythagorean Theorem: a² + b² = c²
Special right: 30-60-90 sides in ratio 1 : √3 : 2
Special right: 45-45-90 sides in ratio 1 : 1 : √2
Sum of angles: always 180°
Circle Formulas
Circles
Area: A = πr²
Circumference: C = 2πr = πd
Arc length: (θ/360°) × 2πr
Sector area: (θ/360°) × πr²
Standard equation: (x − h)² + (y − k)² = r²
3D Solids
The ACT tests volume and surface area of basic 3D shapes. You will never be asked to derive these — just memorize them.
3D Solids
Rectangular prism volume: V = l × w × h
Cylinder volume: V = πr²h
Cone volume: V = ⅓πr²h
Sphere volume: V = (4/3)πr³
Practice · Fundamental
Geometry Quizzes 1–3
Basic triangles, angles, and polygons. 10 questions each.
Start Quiz 1 →
Practice · Intermediate
Geometry Quizzes 4–6
Circles, 3D solids, coordinate geometry. 7 questions each.
Start Quiz 4 →
Practice · Advanced
Geometry Quizzes 7 & 8
Multi-step geometric reasoning at full ACT difficulty. 8 questions each.
Start Quiz 7 →
Related ACT Math Topics
Strengthen the skills that connect to geometry:
- Perimeter, Area & Volume — Dedicated module for area and volume calculation questions
- Distances — Distance formula, midpoint, and coordinate geometry
- Angles — Angle relationships — parallel lines, transversals, polygons
Full Quiz Bank
All 191 ACT Math Quizzes — 100% Free
28 topic modules, 30 timed mini exams, and 20 full-length practice exams. No subscription needed.
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