If the mathematics foundation reaches the university level or above, then the method is as follows.

1, fit the boundary with curve, and then integrate to find the area.

2. Monte Carlo method. Put the object on the regular figure, randomly scatter points, calculate the probability of falling on the target object, and then multiply it by the known area of the regular figure.

If you don't reach college mathematics, then

1, square paper to find the area. Put the object on the grid paper and count the squares covered. The denser the squares, the more accurate they are.

2. Cut-and-fill method, which divides the object into several regular figures, and the irregular areas are approximated by regular figures. The principle of calculating the sum of regular graphic areas is the same as above. add

This method is to decompose an irregular figure into several basic regular figures, calculate their areas respectively, and then add them to find the area of the whole figure.

For example, find the area of the whole figure below.

Bottom line: area of semicircle+area of square = total area.

This method regards the area of irregular figure as the difference of several basic regular figures.

For example, as shown below, find the area of the shaded part.

Bottom line: first find the area of the square, and then subtract the area of the circle inside.