Plasmid Map
Tools

Oligo calculator

Calculate molecular weight from a DNA or RNA sequence, then convert mass, amount or concentration.

01

Your values

Up to 5,000 bases, plain or one FASTA record. DNA: A/C/G/T. RNA: A/C/G/U. For a duplex, enter one strand.

Unmodified, linear molecules with 5′-OH and 3′-OH ends.

02

Example result

Molar mass · molecular weight

5,557.68g/mol

Each base contributes its published unit weight. Subtract 61.96 g/mol once for the unmodified strand’s ends.

Sequence length
18 nt
GC content
55.56%
Base composition
A: 6 · C: 4 · G: 6 · T: 2
Calculation & assumptions

MW = Σ nucleotide unit weights − 61.96

  • Average anhydrous acid-form mass, with a hydroxyl at each end of every strand. Not a sodium-salt or monoisotopic mass.
  • No phosphate ends, circular molecules, labels, modified bases or mixed-base oligos. Use the supplier’s stated mass for those.
  • These calculations do not establish purity, recovery or primer performance. Display rounding is not measurement precision.

From sequence to amount

Enter the sequence as plain text or one FASTA record. Spaces, line breaks and lowercase letters work. Choose DNA or RNA explicitly: T is not silently changed into U. Ambiguous bases, numbers and modification labels are refused.

For double-stranded DNA, enter just one strand. The other is its exact complement; the calculation assumes a fully paired, blunt-ended duplex with hydroxyl ends. It does not describe a circular plasmid, a restriction fragment with phosphate ends, or a pair with overhangs.

How molecular weight is calculated

Add the nucleotide unit weights, then subtract 61.96 g/mol per strand. The result is an average anhydrous acid-form molar mass, numerically equal to the molecular mass in daltons. It is not a monoisotopic mass or a mass including counterions.

Nucleotide DNA unit weight (g/mol) RNA unit weight (g/mol)
A 313.21 329.21
C 289.18 305.18
G 329.21 345.21
T / U 304.20 (T) 306.17 (U)

For a known modified-oligo mass, use the molarity calculator. A supplier's product-specific value takes precedence over this unmodified model.

Worked example: M13 forward primer

The single-stranded DNA sequence GTAAAACGACGGCCAGTG has 18 bases and a calculated molar mass of 5,557.68 g/mol. At 5.47 nmol, that corresponds to 30.401 µg, or 30.4 µg rounded.

The conversions use n = m / MW and c = ρ / MW, after bringing mass into grams and volume into litres. For this primer, 10 ng/µL ≈ 1.7993 µM. These are conversions from the entered quantity, not measurements of purity or recovery.

Prepare the next step

Use the delivered amount in the primer resuspension worksheet to find a stock volume and plan a working dilution. Use the primer Tm calculator for the separate temperature calculation with explicit salt and concentration settings.

Sources and assumptions

DNA unit weights and end correction: Glen Research, The Glen Report 34.1 (2022), page 12. RNA unit weights and hydroxyl ends: Eurogentec oligonucleotide FAQ. Checked October 1, 2026.

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