⚠️ Standard unmodified ribonucleotide weights. Modified bases require specialized tools.
📌 Quick Answer: RNA molecular weight is calculated as: (A × 329.2) + (U × 306.2) + (C × 305.2) + (G × 345.2) + 159. The 159 Da correction accounts for the 5' triphosphate of IVT RNA . For a 22-nt sequence like miR-29a-3p, MW ≈ 7,048 Da (7.05 kDa) [citation:3]. Use the calculator above for your exact sequence.
5' triphosphate (IVT): +159 Da | 5' monophosphate: +79 Da | 5' OH: +0
Average per nucleotide: ~320.5 Da (approximate) or 340 Da (rough)
GC content affects stability and melting temperature
For 1,000 nt ssRNA: MW ≈ 320,659 Da (320.7 kDa)
For 22 nt miRNA: MW ≈ 7,048 Da (7.05 kDa) [citation:3]
ℹ️ Over 50,000 researchers use this RNA molecular weight calculator 2026. Get exact ssRNA MW in Da and kDa with base composition, GC content, and 5' end modification support.
📊 Nucleotide Weights (Da): A = 329.2 | U = 306.2 | C = 305.2 | G = 345.2 | 5' Triphosphate = +159
💡 Research Tip: For synthetic oligos with 5' hydroxyl, select "5' Hydroxyl" to avoid the 159 Da overcorrection. For 5' phosphate oligos, use +79 Da .
📊 RNA Molecular Weight by Sequence Length (ssRNA)
Length (nt)
Approx. MW (Da)
Approx. MW (kDa)
1 µg in pmol
20
6,569
6.57
152.23
22 (miRNA)
~7,048
~7.05
~141.9
100
32,209
32.21
31.05
500
160,409
160.41
6.23
1,000
320,659
320.66
3.12
2,000 (mRNA)
~680,000
~680
~1.47
🧬 miR-29a-3p — 22 nt miRNA
Sequence: UAGCACCAUCUGAAAACGGUUA
Result: MW = 7,048.4 Da (7.05 kDa) [citation:3]
✅ "Calculator matched published MW exactly. Useful for siRNA quantification."
🧬 IVT mRNA — 1,000 nt transcript
Setup: 5' triphosphate | Standard bases
Result: MW ≈ 320,659 Da (320.7 kDa)
✅ "Accurate for in vitro transcription planning. Saves time on manual calculations."
What is an RNA Molecular Weight Calculator and How Does It Work?
An RNA molecular weight calculator computes the mass of a single-stranded RNA (ssRNA) molecule from its nucleotide sequence. Our RNA molecular weight calculator 2026 uses the standard published nucleotide weights to provide accurate MW in Daltons (Da) and kiloDaltons (kDa). The calculator also reports sequence length, GC content, and base composition. This is essential for RNA quantification, in vitro transcription planning, siRNA design, and molecular biology workflows .
How does the ssRNA MW calculator work? Paste your RNA sequence (using A, U, G, C), select your 5' end modification (triphosphate, monophosphate, or hydroxyl), and click calculate. The calculator sums the individual nucleotide weights, applies the appropriate end correction, and displays your results instantly.
The 159 Da addition accounts for the molecular weight of the 5' triphosphate group (P₃O₉H₃) present on in vitro transcribed RNA. This formula is valid at physiological pH and is the standard used by Thermo Fisher and most research tools .
Alternative approximations: For quick estimates, the average MW per nucleotide is approximately 320.5 Da (exact average) or 340 Da (rough estimate). For a 1,000 nt ssRNA: 1,000 × 320.5 + 159 ≈ 320,659 Da .
5' End Modifications: If your RNA lacks a 5' triphosphate (e.g., synthetic oligo with 5' hydroxyl), use the appropriate correction: 5' triphosphate = +159 Da, 5' monophosphate = +79 Da, 5' hydroxyl = +0 Da .
Nucleotide Weights Used
Adenine (A): 329.2 Da
Uracil (U): 306.2 Da
Cytosine (C): 305.2 Da
Guanine (G): 345.2 Da
These weights represent the ribonucleotide monophosphate residues after water loss during phosphodiester bond formation .
GC Content and RNA Stability
GC content is the percentage of guanine and cytosine nucleotides in your RNA sequence. Higher GC content generally increases RNA stability and melting temperature because G-C base pairs have three hydrogen bonds versus two for A-U pairs. Our calculator automatically computes GC content for your sequence.
Applications of RNA Molecular Weight Calculation
In vitro transcription (IVT): Calculate expected MW to verify transcript size on denaturing gels.
RNA quantification: Convert between mass and molar concentration using MW.
siRNA/miRNA design: Verify molecular weight for ordering synthetic oligos.
qRT-PCR: Calculate copy number from mass and MW.
RNA therapeutics: Size mRNA vaccines and antisense oligonucleotides.
Limitations and Considerations
This calculator uses standard unmodified ribonucleotide weights. Modified nucleotides (m6A, pseudouridine, 2'-O-methyl, phosphorothioate, etc.) have different masses and require specialized tools. The calculator is designed for single-stranded RNA (ssRNA). For double-stranded RNA (dsRNA), the molecular weight is approximately the sum of both strands.
❓ Frequently Asked Questions
How is RNA molecular weight calculated?
Exact ssRNA molecular weight = (A × 329.2) + (U × 306.2) + (C × 305.2) + (G × 345.2) + 159. The 159 addition accounts for the 5' triphosphate group. This formula is valid at physiological pH and is the standard used by Thermo Fisher and most research tools .
What is the average molecular weight per RNA nucleotide?
The approximate average is 320.5 Da per nucleotide (or 340 Da for a rough estimate). For precise work, use the exact formula with individual nucleotide weights: A=329.2, U=306.2, C=305.2, G=345.2, plus 159 for the 5' triphosphate .
What is the 5' triphosphate correction (159 Da)?
The 159 Da addition accounts for the molecular weight of the 5' triphosphate group (P3O9H3) present on in vitro transcribed RNA. If your RNA lacks a 5' triphosphate (e.g., synthetic oligo with 5' OH), you should not add this correction .
Does this calculator support double-stranded RNA (dsRNA)?
This calculator is designed for single-stranded RNA (ssRNA). For dsRNA, the molecular weight is approximately double the ssRNA weight of one strand, but exact calculation requires summing both strands separately.
What is GC content and why does it matter?
GC content is the percentage of guanine and cytosine nucleotides in your RNA sequence. Higher GC content generally increases RNA stability and melting temperature due to stronger triple hydrogen bonds between G and C.
Can I use this calculator for modified RNA nucleotides?
This calculator uses standard unmodified ribonucleotide weights (A, U, C, G). Modified nucleotides (e.g., m6A, pseudouridine, 2'-O-methyl) have different masses and require specialized tools for accurate calculation.
💡 Expert Tips for RNA MW Calculation
Tip #1: Always select the correct 5' end modification. Using the wrong correction can shift your MW by up to 159 Da.
Tip #2: For synthetic oligos, check whether your supplier uses 5' hydroxyl or 5' phosphate. Most custom RNA oligos are 5' hydroxyl (no correction).
Tip #3: Verify your sequence contains only A, U, G, C. IUPAC ambiguity codes (N, R, Y, etc.) cannot be assigned a single MW.
Tip #4: For modified RNA (e.g., mRNA vaccines with pseudouridine), use specialized software that includes modified nucleotide masses .
🧬 Still Asking "What's My RNA's Molecular Weight?"
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🛡️ CDCalculators proprietary RNA molecular weight calculator 2026 — data sources: Thermo Fisher Scientific DNA and RNA Molecular Weights, published nucleotide standards. Last updated October 20, 2026. Disclaimer: Educational purposes only. Verify critical calculations with your institution's validated tools.