Kilodaltons to Daltons Converter
Common Conversions
| kDa | Da |
|---|---|
| 0.1 | 100 |
| 0.5 | 500 |
| 1 | 1000 |
| 5 | 5000 |
| 10 | 10000 |
| 25 | 25000 |
| 50 | 50000 |
| 66.5 | 66500 |
| 100 | 100000 |
| 150 | 150000 |
| 500 | 500000 |
| 1000 | 1000000 |
Why this conversion matters in chemistry
Antibody intact-mass characterization runs across this conversion. An IgG1 therapeutic written as 148.5 kDa in the structural literature shows up as a 148,500 Da peak (or a series of glycoform peaks separated by ~162 Da each for hexose mass) on a deconvoluted intact-mass ESI-MS spectrum. The multiplier of 1000 falls cleanly out of the kilo prefix. What it really is: the unit jump between the kDa convention biochemists use for protein-scale molecules and the Da resolution mass spectrometry actually measures.
Formula
Where the factor comes from
The dalton also answers to u, the unified atomic mass unit, yet only one of those names takes prefixes in practice: kilodalton is everywhere in protein work while kilo-u is written by nobody. That asymmetry is why this conversion exists as a routine step at all. The prefix does what prefixes do — kilo is 10³ exactly — rescaling the unit without reaching into the dalton's own definition, which points at one twelfth of the mass of a free carbon-12 atom in its ground state. The dalton's value in kilograms is a measured quantity that shifts slightly with each CODATA adjustment; the ratio between kilodalton and dalton does not, and never has. Expanding 1 kDa to 1000 Da adds three digits of place value. Whether it adds any information is a separate question the arithmetic cannot answer.
Precision and significant figures
Expanding is where digits get invented. A 150 kDa value from a gel or a sizing column supports three significant figures at best, and writing it as 150,000 Da presents six, three of them trailing zeros a reader has no way to distinguish from measured ones. Scientific notation settles it: 1.50 × 10⁵ Da states exactly what was known. The opposite case is equally real — a deconvoluted intact mass on that same protein can be good to tens of parts per million, a few daltons out of 150,000, and collapsing it back to 150 kDa throws away the digits the run was performed to obtain. The dalton form exists for measurements like that one; drop back to kilodaltons only when the extra places were never real.
Worked Examples
BSA — the calibration anchor for many protein-mass quantitation curves.
The factor anchor — about a 9-residue peptide expressed in Da.
An IgG antibody — the per-Da figure for an intact-mass measurement.
A 10 kDa MWCO ultrafiltration cutoff — the membrane spec written in Da on the cassette.
Common mistakes
One Da value for a heterogeneous glycoprotein
Expanding a glycoprotein's kDa figure into daltons implies a single mass where the intact-mass spectrum shows a family of peaks differing by individual sugar residues. Quoting one dalton value picks a representative out of a distribution. The polypeptide backbone has a definite mass; the molecule as isolated does not, and the figure should say which of the two it means.
Monoisotopic comparison above ten kilodaltons
Below a few kilodaltons a spectrum resolves the isotope envelope and a monoisotopic peak is meaningful. Past roughly 10 kDa the envelope broadens until the all-light-isotope species is a vanishing fraction of the population, so the reported mass is necessarily an average. A kilodalton value expanded to daltons and checked against a calculated monoisotopic mass mismatches by tens of daltons for that reason alone.
MWCO ratings are not sharp cutoffs
An ultrafiltration membrane labelled 10 kDa, printed as 10,000 Da on the cassette, does not pass everything lighter and retain everything heavier. The rating is a nominal retention figure, and molecular shape, charge and solution concentration all shift where a given species actually partitions. Converting the label to daltons produces an exact number for a specification that was never sharp to begin with.