Tadpole-shaped single-chain nanoparticles (TSCNPs) are useful soft building blocks for nanotechnology composed of a flexible polymer chain tethered to an intramolecularly folded single-chain nanoparticle. We disclose herein valuable structure-size relationships for a priori TSCNP design depending on tail length, which are validated by experimental data from multiple TSCNP systems, allowing, for the first time, the prediction of TSCNP size before synthesis.