Well obviously it depends on the size of your body!
America’s National Institutes of Health suggests an answer of approximately 37.3 million million cells for a typical adult human, which seems a bit boggling but gives a reasonable estimate of body weight.
If we assume each cell is approximately 0.01 mm x 0.01 x 0.01 mm in size then that corresponds to a volume of approximately 0.037 cubic metres or 37 litres.
If cells have the same density as water, they would account for roughly 37 kg – about half the weight of a typical person.
This seems reasonable to me.
Picture: Cells in a trichrome-stained photomicrograph