The ratio of the diameters of moon and earth is nearly

The diameter of the Moon is approximately $3,474\text{km}$, while the equatorial diameter of the Earth is approximately $12,742\text{km}$. Taking the ratio:
$$\text{Ratio}=\frac{3,474}{12,742}\approx 0.272\approx \frac{1}{4}$$

Thus, the ratio of the diameters of the Moon and the Earth is nearly $1:4$.