The following three laws of proportionality apply to the characteristic field of a fan. These relationships are also called affinity laws.
\frac{q_{V,I}}{q_{V,II}}=\left(\frac{D_I}{D_{II}}\right)^3\cdot\frac{n_I}{n_{II}}
\frac{p_I}{p_{II}}=\frac{\rho_I}{\rho_{II}}\cdot\left(\frac{D_I}{D_{II}}\right)^2\cdot\left(\frac{n_I}{n_{II}}\right)^2
\frac{P_I}{P_{II}}=\frac{\rho_I}{\rho_{II}}\frac{}{}\cdot\left(\frac{D_I}{D_{II}}\right)^5\cdot\left(\frac{n_I}{n_{II}}\right)^3
If only individual variables change, these equations can be simplified accordingly. This will be discussed in the following chapter.