Thanks Chris,
How do you know how many places are significant. Since it is in cm^3 surely only 1 place would be significant.
There are 100 cm in a metre and 1000m in a km so that is 100,000 cm in a km
that is 100,000*100,000 = $$10^5*10^5=10^{10}$$ cm^2 in a km^@
so
The Pacific Ocean has a surface area of 1.66242 x 108 km2
$$1.66242 \times 10^{8+10}=1.66242 \times 10^{18} cm^2$$
and an average depth of 3.940 x 103m.
which is $$3.940\times 10^{3+2}=3.940\times 10^{5}\;\;cm \qquad Edited$$
Volume is surface area x depth
$${\mathtt{1.662\: \!42}}{\mathtt{\,\times\,}}{\mathtt{3.94}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{{\mathtt{18}}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{{\mathtt{5}}} = {\mathtt{654\,993\,480\,000\,000\,000\,000\,000}}$$
$$\\$Volume = $ 6.549934800 \times 10^{23}\;\;cm^3\qquad Edited$$
I don't know how many of these are significant :/
Maybe I will go for 4 since depth has 4
$$\\$Volume = $ 6.550 \times 10^{23}\;\;cm^3\qquad Edited$$ (Thanks Chris) I think I like 4 sf :))
