What people use the Biosynth calculator for
Biosynth is a peptide and biochemical supplier whose website hosts a sequence-properties calculator: paste an amino acid sequence, get back the average molecular weight, extinction coefficient at 280 nm, and net charge at neutral pH. It is a useful tool when you are checking a custom-synthesised peptide or working at the bench.
The thing it does not cover is the next stage: turning a powdered vial into a measured dose. Reconstitution volume, concentration math, mL per dose, and syringe units are all outside its scope. That gap is where PepSync exists.
How PepSync and Biosynth's calculator compare
A factual comparison, not a critique. Different tools for different jobs.
| Capability | Biosynth | PepSync |
|---|---|---|
| Peptide molecular weight from sequence | Yes | Yes (tool) |
| Extinction coefficient at 280 nm | Yes | Yes |
| Net charge / isoelectric point | Yes | Yes |
| Vial reconstitution math (mg, mL, mg/mL) | No | Yes |
| Dose volume from target dose | No | Yes |
| Syringe unit conversion (U-100, U-50, U-40) | No | Yes |
| Saved protocols + dose reminders | No | iOS app |
| Free, no signup, no ads | Yes | Yes (web) |
When PepSync is the better choice
If you are reconstituting vials of compounded semaglutide, tirzepatide, retatrutide, BPC-157, TB-500, CJC-1295/Ipamorelin or similar peptides and need to convert vial strength + BAC water volume + target dose into a draw volume and syringe units, PepSync covers that workflow directly. The web calculators are free; the iOS app stores the setup so you do not re-derive it every time.
If you are working with a custom synthesised peptide sequence and need just molecular weight, charge, or extinction coefficient, either tool works. PepSync's molecular weight calculator covers that case.