Which is bigger RNA or DNA?

DNA is bigger than RNA.
DNA stands for Deoxyribonucleic Acid, and RNA stands for Ribonucleic Acid. DNA is a double-strand helix with a long chain of nucleotides, whereas RNA is only a single-strand helix with a shorter chain of nucleotides. Thus, their shapes and appearance look quite different.
Another main difference between DNA and RNA is that DNA contains the sugar deoxyribose, whereas RNA contains the sugar ribose (this is apparent in their names). The ribose contained in RNA is considered "normal" because it contains an oxygen atoms that is attached to the carbon atoms. However, the deoxyribose in DNA is considered a different type of sugar because it lacks an oxygen atom.
Their bases are also slightly different; both DNA and RNA contain the bases adenine, guanine, and cytosine, but DNA's fourth base is thymine, and RNA's fourth base is uracil. 
 
https://www.ncbi.nlm.nih.gov/books/NBK26887/