Skip to main content
Pearson+ LogoPearson+ Logo
All Calculators & ConvertersAll calculators

Choose a mode and enter values

A260 → DNA concentration: best for NanoDrop-style UV measurements.

Mode:

Enter the absorbance at 260 nm from your spectrophotometer.

If you measured undiluted sample, use 1. For a 1:10 dilution, use 10.

If provided, we’ll estimate purity via 260/280 (~1.8 ideal for DNA) and 260/230 (~2.0–2.2).

If you enter a volume, we’ll also estimate the total DNA mass in the tube.

Chips prefill common scenarios and auto-calculate; you can tweak values and recalculate.

Result:

No results yet. Choose a mode, enter values, and click Calculate or use a quick pick.

Unit reminder: 1 µg/mL = 1 ng/µL, 1 nM = 10⁻⁹ mol/L.

How to use this calculator

  • A260 → concentration: enter A260, dilution factor, nucleic acid type, optional purity readings (A280, A230), and optional sample volume in µL.
  • Mass → molar: enter DNA concentration in ng/µL and fragment length in base pairs.
  • Molar → mass: enter DNA concentration in nM and fragment length in base pairs.
  • Quick picks: click a chip to prefill typical lab scenarios; we auto-calculate and you can edit values and click Calculate again if needed.

Units: A260 is unitless, concentration is reported in µg/mL and ng/µL, and molar concentration in mol·L⁻¹ and nM.

Formula & Equation Used

1. A260 → mass concentration:

C= A260 ×f ×d

Here C is concentration in µg·mL⁻¹, f is the factor (e.g. 50 µg·mL⁻¹ per A260 for dsDNA), and d is the dilution factor. Because 1 µg·mL⁻¹ = 1 ng·µL⁻¹, the same numeric value applies in ng/µL.

2. Mass (ng/µL) → molar (nM):

cg/L = cng/µL × 10⁻3 M= 660×Nbp cmol/L = cg/L M cnM = cmol/L × 10⁹

We approximate dsDNA molar mass as 660 g·mol⁻¹ per base pair, so M ≈ 660 × Nbp.

3. Molar (nM) → mass (ng/µL):

cmol/L = cnM × 10⁻9 cg/L = cmol/L ×M cng/µL = cg/L × 10³

Again M ≈ 660 × Nbp for dsDNA.

Example Problems & Step-by-Step Solutions

Example 1 — A260 → ng/µL for dsDNA

A dsDNA sample gives A260 = 0.85 at a 1:10 dilution. Using the dsDNA factor 50 µg·mL⁻¹:
C = 0.85 × 50 × 10 = 425 µg·mL⁻¹ = 425 ng·µL⁻¹.

Example 2 — Convert 50 ng/µL, 1000 bp to nM

For a 1000 bp dsDNA fragment, M ≈ 660 × 1000 = 6.60×10⁵ g·mol⁻¹. 50 ng·µL⁻¹ = 0.050 µg·µL⁻¹ = 0.050 mg·mL⁻¹ = 0.050 g·L⁻¹.
c = 0.050 / (6.60×10⁵) mol·L⁻¹ ≈ 7.58×10⁻⁸ mol·L⁻¹ = 75.8 nM.

Example 3 — Convert 25 nM, 5000 bp to ng/µL

For a 5000 bp dsDNA fragment, M ≈ 660 × 5000 = 3.30×10⁶ g·mol⁻¹. 25 nM = 25×10⁻⁹ mol·L⁻¹.
c = 25×10⁻⁹ × 3.30×10⁶ g·L⁻¹ ≈ 0.0825 g·L⁻¹ = 82.5 ng·µL⁻¹.

Frequently Asked Questions

Q: What factor should I use for dsDNA, ssDNA, and RNA?

For standard UV measurements at 260 nm, use 50 µg·mL⁻¹ per A260 for dsDNA, 33 µg·mL⁻¹ for ssDNA, and 40 µg·mL⁻¹ for RNA. If your protocol uses a different extinction coefficient, choose “Custom factor” and enter it manually.

Q: How accurate are these calculations?

The calculator assumes clean nucleic acid samples and an average base composition. Contaminants (proteins, phenol, salts) or unusual sequences can affect A260 readings. For high-precision work, combine A260-based estimates with gel quantification or fluorometric assays.

Q: Why do you use 660 g·mol⁻¹ per base pair?

660 g·mol⁻¹ per base pair is a widely used average molar mass for dsDNA, based on typical nucleotide composition. It provides a good approximation for most lab calculations and is standard in many molecular biology protocols.