If you know an area of a single raster cell in projection (which should be 30 m × 30 m = 900 sq meters or 0,09 ha), then for each class you can multiply the cell area with the cell count.

For example, class 1 has 14 478 cells, multiplied by 0,09 ha gives the area of 1303 ha.

Alternatively, total area x percent of the area.

it will calculate it by using the size of pixel multiplied by the no of pixels for each class.

regards

Thanks to u all :)

add a new column called area and multiply the column of "counts" with the area of a pixel (pixel size^2)

Hy Gazi, is simple, first be sure your shape of clasification is not in Geographical Coordenates, it mus be in UTM, then open your table (about your shape file with the clasification), then click in the left corner, click in the "Add Fiel", choose name (like ha, km) and in Type choose Double, then click ok.

Now in the new Field click with right mouse buton, choose Calculate Geometry, in Property choose area and pick up the units, coul be hectareas or kilometers.

Regards

Hi Andres, note that UTM is a conformal projection which does not preserve areas. Being locally optimized there are no large distortion, but for more precise area  computation I would rather use an equal area projection (especially if your image fall between two UTM zone)

This formulae may be useful. For landsat image for instance.

Area in ha = 30*30*count/10000.

Perc= count/sum*100.

Same to Aigbokhan John

This formula may be useful. For Landsat image for instance.

Area in ha = 30*30*count/10000.

Perc= count/sum*100.

I am prepared this formula in my work

Convert Raster to vector then you will have area of each classes and Riht click on Area the Calculate Geometry in (Ha)

Or (Resolution *Resolution)*0.0001

or Calculate Raster Zonal Statics then tabulate area