Would be very helpful if you could specify what geometric object you would like to know the area of.

Nontheless here are a few formula for the area of polygons and circles:

square: A = s^{2}, s: length of one side

rectangle: A = lw, (length * width)

circle: A = pi * r^{2}, r: radius

triangle: A = bh/2, b: base, h: height

quadrilateral: A = pq sin t, (p and q are the length of the diagonals, and t is the angle between them)

parallelogram A = bh (base * heigth)

rhombus: A = pq/2 (p and q are the length of the diagonals)

trapezoid: (a + b)h/2 (a and b are the length of the parallel sides, h is the heigth)

ellipse: pi * ab, (a and b are the semi-major and the semi-minor axes)