How small is a microRNA molecule?

Mature microRNA molecules are approximately 19–25 nucleotides in length — they are among the smallest functional RNA molecules known in biology. For reference, a single nucleotide is about 0.33 nanometers long, so a 22-nucleotide miRNA is roughly 7.3 nanometers end-to-end. A human hair is about 100,000 nanometers wide. Despite their tiny size, miRNAs have enormous biological impact — each one can regulate dozens or even hundreds of different target mRNAs, and collectively they regulate the expression of more than 60% of all human protein-coding genes. The nanopore used to detect them (approximately 1.4 nm in diameter) is perfectly sized to allow a tagged single-stranded miRNA to thread through and produce a measurable current blockage event.