Calculators

Quadratic Equation Solver
Enter the three values of a quadratic equation and this calculator will give the two roots. 
Right Angled Triangles
This calculator asks for any two values and then gives all three side lengths, all three angles and the area of the triangle. 
Triangles
Calculates all three size lengths, the angles, perimeter, area, inradius and circumradius. 
Percentages
This calculator gives the percentage increase or decrease of two values. 
Volume
Converts between cubic metres and 18 other popular measures of volume. 
Temperature
Converts between Kelvin, Celcius, Fahrenheit, Reaumur, and Rankine. 
Spheres

Sectors
Calculates the radius, diameter, circumference, surface area and volume of a sphere. 
Roman numeral converter
Type in a figure in Roman Number format or type any number and this calculator will convert. 
Rectangles
This calculator calculates the edge sizes, perimeter diagonal and area of a rectangle. 
Pyramids
This calculator asks for any two values and then gives the base edge, perpendicular height, slant edge, perpendicular height, slant edge length, slant height, volume and the angle between the base and the triangular sides. 
Polygons
When given the number of edges and their lengths, this calculator will give the area and both the inradius and circumradius. This page also gives a handy table of polygon names for shapes ranging from 3 to 12 sides. 
Mass 2
This calculator converts between pounds and ounces and kilograms, grams and milligrams. 
Mass 1
Type in any mass size and this calculator will convert the value to 17 different measures. 
Loan repayment
This calculator calculates repayments where a sum of money is borrowed at fixed intervals with interest being added at the end of each interest interval. It calculates the instalments so that the last payment matches the final payment owing. 
Length 2
The calculator converts between feet and inches, metres, centimetres and millimetres. 
Length 1
Type in the length, choose the units and this calculator will convert your value to 19 different measures. 
Growth and decay
This calculator uses the compound and simple interest formulae to calculate future value (FV) of a data value (both growth and decay) given present value (PV), rate of change (i) and the number of periods. 
Fractions

Equivalent fractions
This gives a table of fractions and decimals. By looking along each row you can see a line of equivalent fractions for the most common fraction values. 
Ellipses
Calculates the major and minor axes, eccentricity, area, foci distance and loop length. 
Cylinders
Calculates diameter, height, volume, curved surface area and total surface area. 
Cubes
Calculates the edge length, space diagonal, surface area and volume. 
Cones
Calculates the base radius, perpendicular height, slant length, curved surface area, volume and angle between the base and the slanted side. 
Circles
Calculates radius, diameter, circumference, area and the semicircle area