Unit reference tables for the biochemistry lab
Every prefix and conversion factor used across this site, plus a converter that shows one value in all units at once.
Any unit → every unit
Pick a quantity, type a value, read it in every unit.
| Unit | Value | Factor to base |
|---|
SI prefixes
| Prefix | Symbol | Factor | Where you meet it |
|---|---|---|---|
| mega | M | 10⁶ | MDa for large complexes; Mbp for genomes |
| kilo | k | 10³ | kDa for proteins; kb for DNA |
| — | — | 10⁰ | gram, litre, mole, molar |
| deci | d | 10⁻¹ | mg/dL in clinical chemistry |
| centi | c | 10⁻² | cm path length in a cuvette |
| milli | m | 10⁻³ | mL, mg, mM — the everyday scale |
| micro | µ | 10⁻⁶ | µL, µg, µM — the pipetting scale |
| nano | n | 10⁻⁹ | ng of DNA, nM ligand, nmol oligo |
| pico | p | 10⁻¹² | pmol in a ligation, pM antibody |
| femto | f | 10⁻¹⁵ | fmol in mass spec, fg of genomic DNA |
| atto | a | 10⁻¹⁸ | aM detection limits, ag per plasmid copy |
Equivalences worth knowing by heart
| These are all the same | Because |
|---|---|
1 g/L = 1 mg/mL = 1 µg/µL | Numerator and denominator both scale by 1000 |
1 mg/L = 1 µg/mL = 1 ng/µL | Same reason, one decade down |
1 % (w/v) = 10 g/L | 1 g per 100 mL is 10 g per 1000 mL |
1 ppm = 1 mg/L = 1 µg/mL | Only when the density is 1.00 g/mL |
1 Da = 1 g/mol | Definition of the unified atomic mass unit |
1 kDa = 1000 g/mol | A 50 kDa protein is 50 000 g/mol |
1 U = 16.67 nkat | 1 µmol/min ÷ 60 s = 1.667 × 10⁻⁸ mol/s |
1 M = 10³ mM = 10⁶ µM = 10⁹ nM | Each prefix step is 1000× |
Physical constants
| Constant | Symbol | Value |
|---|---|---|
| Avogadro constant | NA | 6.022 140 76 × 10²³ mol⁻¹ (exact) |
| Gas constant | R | 8.314 462 618 J mol⁻¹ K⁻¹ |
| Gas constant (cal) | R | 1.987 cal mol⁻¹ K⁻¹ |
| Boltzmann constant | kB | 1.380 649 × 10⁻²³ J K⁻¹ (exact) |
| Faraday constant | F | 96 485.33 C mol⁻¹ |
| Planck constant | h | 6.626 070 15 × 10⁻³⁴ J s (exact) |
| Standard gravity | g | 9.806 65 m s⁻² (exact) |
| RT at 25 °C | RT | 2.479 kJ/mol = 0.5925 kcal/mol |
| RT·ln(10) at 25 °C | — | 5.708 kJ/mol per log unit |
| Water, molar concentration | — | 55.34 M at 25 °C |
| Water, density at 25 °C | ρ | 0.997 047 g/mL |
Energy and temperature
| Convert | Multiply by | Example |
|---|---|---|
| kcal → kJ | 4.184 | 1 kcal/mol = 4.184 kJ/mol |
| kJ → kcal | 0.2390 | 10 kJ/mol = 2.39 kcal/mol |
| Kd → ΔG° at 25 °C | ΔG° = RT·ln(Kd) | Kd = 1 nM → −51.2 kJ/mol |
| °C → K | + 273.15 | 25 °C = 298.15 K |
| °C → °F | × 9/5 + 32 | 37 °C = 98.6 °F |
Nucleic acid and protein rules of thumb
| Rule | Value |
|---|---|
| Average MW per base pair of dsDNA | 617.96 g/mol |
| Average MW per amino-acid residue | 110 g/mol |
| Protein length from molecular weight | MW (Da) ÷ 110 ≈ residues |
| Coding sequence length from protein length | residues × 3 + 3 (stop) bp |
| 1 µg of 1 kb dsDNA | 1.52 pmol = 9.1 × 10¹¹ molecules |
| 1 A₂₆₀ unit of dsDNA | 50 µg |
| 1 A₂₆₀ unit of oligo | 33 µg |
| 1 A₂₆₀ unit of RNA | 40 µg |
| Rise per base pair, B-DNA | 0.34 nm |
| Base pairs per turn, B-DNA | 10.5 |
A note on the micro sign
Two characters look identical in most fonts: the micro sign µ (U+00B5) and the Greek
small letter mu μ (U+03BC). SI specifies the Greek mu, but the micro sign is what
most keyboards and legacy encodings produce. They are different code points, so a search or a
script that matches one will silently miss the other. Everything on this site uses U+00B5.
Frequently asked questions
What are the SI prefixes used in biochemistry?
Going down from the base unit: milli (10⁻³), micro (10⁻⁶), nano (10⁻⁹), pico (10⁻¹²), femto (10⁻¹⁵) and atto (10⁻¹⁸). Going up: kilo (10³) and mega (10⁶).
Is 1 µg/µL the same as 1 mg/mL?
Yes — both equal 1 g/L. Multiplying numerator and denominator by 1000 leaves the ratio unchanged, which is why µg/µL, mg/mL and g/L are interchangeable.
How many µM are in 1 mM?
1000. Each SI prefix step in this range is a factor of 1000: 1 M = 10³ mM = 10⁶ µM = 10⁹ nM = 10¹² pM.