Molecular weight calculator — Input a protein (amino acid) or nucleic acid (DNA/RNA nucleotide) sequence and the tool sums each residue/nucleotide mass to give MW in Da/kDa.

(1) Verify recombinant protein MW during purification (SDS-PAGE band check) (2) Pre-calculate target mass for mass spec (MALDI/ESI) (3) Convert µg ↔ pmol for synthesized DNA/RNA oligos (4) Estimate total size of fusion proteins (antibody, His-tag, GFP, etc.)

① Choose sequence type (Protein / DNA / RNA) ② Enter sequence (protein: 1-letter code ACDEFGHIKLMNPQRSTVWY, nucleic: ATGC or AUGC) ③ Auto-calculated output: • Length (residues) • MW (Da, kDa) • Protein: additionally shows pI, extinction coefficient at 280 nm Spaces and newlines auto-removed. Lowercase auto-uppercased.

Example 1) GFP (238 aa, MASKGEELFT...) → MW ≈ 26.9 kDa, pI ≈ 5.7 → Expect ~27 kDa band on SDS-PAGE Example 2) 20-mer ssDNA primer 5'-ATGCGTACGTTAGCATCGAT-3' → MW ≈ 6,128 Da → 100 µM stock × 1 mL = 612.8 µg needed