Gibson Assembly Volume Calculator
Estimate how much vector, inserts, water, and 2X Gibson mix to add for a single reaction. This tool assumes double-stranded DNA and uses 650 g/mol per bp.
DNA Inputs
| Fragment | Length (bp) | Concentration (ng/µL) |
|---|---|---|
| Vector (required) | ||
| Insert 1 | ||
| Insert 2 (optional) | ||
| Insert 3 (optional) | ||
| Insert 4 (optional) |
Note: If computed water is negative, your DNA is too dilute or target fmol is too high for the selected reaction volume.
What this Gibson assembly calculator does
This calculator helps you convert a molar design goal into practical pipetting volumes. Instead of guessing DNA mass in ng, you define a target amount of vector in fmol, choose an insert:vector molar ratio, and enter each fragment’s concentration. The tool then computes:
- DNA mass (ng) needed for each fragment
- Pipetting volume (µL) for each stock
- Total DNA volume in the assembly half-reaction
- Required water and 2X Gibson master mix volumes
Why molar ratios matter in Gibson assembly
Gibson assembly is fundamentally a stoichiometry problem. The exonuclease, polymerase, and ligase can only do their jobs efficiently when the fragments are present in near-optimal relative amounts. If insert is too low, vector may re-circularize or remain unproductive. If insert is too high, non-productive complexes can dominate, especially in multi-fragment assemblies.
A common starting point is 2:1 or 3:1 insert:vector for each insert. The best ratio depends on overlap quality, DNA purity, fragment count, and transformation efficiency. This page gives a practical baseline you can tune experimentally.
Formula used
Converting DNA mass to moles
For double-stranded DNA, an approximate molecular weight is 650 g/mol per bp.
pmol = ng × 1000 / (bp × 650)
Rearranged for target mass:
ng = pmol × bp × 0.65
Calculator assumptions
- Vector target amount is entered in fmol and converted to pmol.
- Each insert is assigned the same insert:vector molar ratio.
- 2X Gibson master mix is used at 1:1 with DNA+water solution (half the final reaction volume).
- Any insert row with missing or zero values is ignored.
How to use this tool in practice
- Set final reaction volume (10 µL or 20 µL are common).
- Choose vector target fmol (often 20–100 fmol depending on protocol).
- Choose insert:vector ratio (start with 2:1 each insert).
- Enter vector and insert lengths and stock concentrations.
- Click calculate, then pipette the suggested volumes.
Troubleshooting and optimization tips
If water volume is negative
Your DNA volume exceeds the allowed pre-mix half-volume. You can fix this by lowering target fmol, reducing fragment count, concentrating DNA, or increasing total reaction volume if your protocol allows it.
If colonies are low
- Verify overlap design (typically 20–40 bp with reasonable GC balance).
- Clean up PCR products to remove primers, salts, and dNTP carryover.
- Use fresh competent cells and include a transformation control.
- Try 2:1 and 3:1 ratios in parallel.
- Lower total DNA if background is high.
For multi-fragment assemblies
As fragment count rises, assembly complexity increases quickly. Keep overlaps unique, avoid repetitive junctions, and reduce fragment number when possible (for example by pre-assembling modules). In many workflows, assembling 2–4 fragments at a time is more reliable than doing 6+ in one reaction.
Good lab habits for reliable results
- Quantify DNA with a method suitable for your concentration range.
- Record lot, concentration, and dilution history for each fragment.
- Avoid repeated freeze-thaw cycles of master mix and DNA stocks.
- Always run positive and negative controls when optimizing conditions.
Educational use notice: This calculator provides planning estimates and does not replace your kit manufacturer’s protocol or institutional SOPs.