You can choose any side to be the base. It need not be the one drawn at the bottom of the triangle. The altitude must be the one corresponding to the base you choose. The altitude is the line perpendicular to the selected base from the opposite vertex.
In the figure above, one side has been chosen as the base and its corresponding altitude is shown.
| ENTER ANY TWO VALUES | ||
| Base | clear | |
| Altitude | clear | |
| Area | clear | |
Use the calculator above to calculate the area of a triangle
Enter any two values and the other will be calculated. For example: enter the base and altitude and press 'Calculate'. The area will be calculated.
Similarly, if you enter the area and base, the altitude needed to get that area will be calculated.
| If you know: | Use this |
| Base and altitude | "Half base times height" method |
| All 3 sides | Heron's Formula |
| Two sides and included angle | Side-angle-side method |
| x,y coordinates of the vertices | Area of a triangle- by formula (Coordinate Geometry) Area of a triangle - box method (Coordinate Geometry) |
| The triangle is equilateral | Area of an equilateral triangle |
In the figure above, click on "freeze altitude". As you now drag point A, notice that the area does not change. The area is dependent on the base and height, and neither of them changes as you move the top vertex side-to-side. Therefore, all the triangles you can create this way have the same area.