What this RNA molecular weight calculator does
This tool estimates the molecular weight of a single-stranded RNA oligonucleotide directly from sequence. Paste your RNA sequence, click calculate, and you instantly get:
- Total molecular weight (g/mol and kDa)
- Nucleotide length
- Base composition (A, C, G, U counts)
- GC percentage
- Optional conversion from micrograms to nmol/pmol
How the calculation works
The calculator uses residue masses (in g/mol) for each RNA nucleotide in a polymer context:
- A = 329.21
- C = 305.18
- G = 345.21
- U = 306.17
Then it adds a terminal water mass (18.015 g/mol) to represent strand ends. If you select 5′ phosphate and/or 3′ phosphate, an additional 79.0 g/mol is added per phosphate group.
Formula used
MW = Σ(residue masses) + 18.015 + terminal phosphate adjustments
This gives a practical estimate suitable for routine laboratory planning and molar conversions.
Why RNA molecular weight matters
Knowing molecular weight helps you move between mass and moles, which is essential for most molecular biology workflows. Typical use cases include:
- Preparing RNA standards for qPCR or RT-qPCR
- Dosing synthetic RNA in cell transfection experiments
- Calculating molar ratios for ligation or assembly steps
- Setting up in vitro transcription or RNA-protein binding studies
Example workflow
Step 1: Enter sequence
Suppose your RNA is AUGGCUAACGUA.
Step 2: Calculate MW
The tool counts each base, computes total molecular weight, and reports the value in both g/mol and kDa.
Step 3: Convert sample mass to amount
If you have 2.0 µg of the oligo, enter that value to estimate how many nanomoles and picomoles are present.
Tips for accurate use
- Use only sequence letters (A/C/G/U). Any invalid symbols should be removed.
- If your sequence includes thymine, the calculator converts T to U automatically.
- Be consistent about terminal chemistry: include phosphates only if they are present in your actual molecule.
- For heavily modified RNA, this basic model may underestimate or overestimate true MW.
Frequently asked questions
Does this support modified bases?
No. This version is for standard RNA bases only. Chemically modified nucleotides require custom mass corrections.
Can I paste multiline FASTA-like text?
Yes, as long as it only contains valid sequence letters. Spaces and line breaks are ignored.
Is this for dsRNA or ssRNA?
The calculator computes one strand at a time. For double-stranded RNA, calculate each strand and sum the two values.
Final note
This RNA molecular weight calculator is designed for fast bench-side estimates. For regulated workflows, vendor-specific formulas and exact modification masses should be applied during final documentation.