How to pick the right area or volume calculator
Match the tool to the shape, not to the word in the question. For flat shapes the Rectangle Area Calculator, Triangle Area Calculator and Area of a Circle Calculator cover most of what comes up, and trapezoids and regular polygons have their own tools because those formulas are easy to misremember.
For solids, decide whether you need the space inside or the skin outside. The Cylinder Volume Calculator and Sphere Volume Calculator give capacity, while surface area tools give material. Keep every input in the same unit — mixing inches and feet is the single most common source of a wrong answer.
What to use when you are stuck on a triangle
It depends on what you know. With a right angle and two sides, the Hypotenuse Calculator applies Pythagoras directly, and the Right Triangle Calculator fills in remaining sides, angles and area from any two known values.
Without a right angle you need the general laws. Use the Law of Sines Calculator when you have an angle paired with its opposite side, and the Law of Cosines Calculator when you have two sides and the angle between them, or all three sides. If you end up with a ratio and need the angle back, the Arctangent Calculator reverses the trig function.
Working with fractions, percentages and roots
These are the topics people quietly forget after school. The Fraction to Decimal Calculator converts a fraction into a decimal you can type into anything, and the Fraction Simplifier Calculator reduces a fraction to lowest terms using the greatest common factor.and the Mixed Number to Improper Fraction Calculator handles the conversion recipes and measurements usually need.
For percentages, be precise about which one you want: the Percentage Calculator finds X% of a number, while the Percentage Change Calculator compares an old value with a new one. Those are different questions with different answers, and mixing them up is behind many wrong discount figures.
Frequently asked questions
- What is the difference between area and perimeter?
- Area is the space inside a shape, measured in square units; perimeter is the distance around its edge, measured in ordinary length units. You would use area to buy carpet for a room and perimeter to buy skirting board for the same room.
- How do you calculate percentage increase?
- Subtract the old value from the new, divide by the old value, then multiply by 100. Going from 40 to 50 is (50 − 40) ÷ 40 × 100 = 25%.
- How do I find the GCF and LCM of two numbers?
- The greatest common factor is the largest number that divides both, and the least common multiple is the smallest number both divide into. Break each number into prime factors: shared factors give the GCF, and all factors at their highest power give the LCM.
- When do I use radians instead of degrees?
- Radians are the standard in calculus, physics and most programming languages, while degrees are used in geometry, navigation and construction. A full circle is 360 degrees or 2π radians.
- What is the quadratic formula used for?
- It solves any equation in the form ax² + bx + c = 0 for x, including cases that will not factor neatly. The discriminant b² − 4ac tells you in advance whether there are two real roots, one, or none.