What prime lengths are used for RSA?
When you multiply an $n$-bit integer by an $m$-bit integer, the product is an $(m+n-\epsilon)$-bit integer, with $\epsilon \leq 1$.

For RSA the security recommendations specify that secret factors of the public modulus must be of approximately the same size. If the difference in the number of bits is modest (less than a machine granularity) it could be approved.

There is also another suggestion from Shamir about generation of RSA keys for paranoid, which recommends for example a prime $p$ of say $1000$ bits and the other prime $q$ of $5000$ bits.