NEB Double Digest Reaction Planner
Enter your reaction setup to calculate DNA, buffer, enzyme, and water volumes. This tool follows common NEB-style digest planning rules (units per µg DNA and enzyme-volume/glycerol checks).
How this NEB double digest calculator helps
A double digest is simple in principle: combine DNA, buffer, two restriction enzymes, and water. In practice, errors usually come from one of three things: too much enzyme volume, incompatible conditions, or wrong DNA loading. This calculator solves the volume math quickly so you can focus on enzyme compatibility and downstream cloning strategy.
It is designed for everyday bench planning when you already know your enzymes and want a clean recipe for a single tube reaction.
What the calculator computes
Core reaction components
- DNA volume from total DNA mass and stock concentration.
- Buffer volume to reach 1X final concentration.
- Each enzyme volume based on desired units per microgram DNA.
- Water volume needed to hit total reaction volume.
Practical quality checks
- Total enzyme volume percentage of final reaction volume.
- Estimated glycerol percentage (assuming 50% glycerol enzyme stocks).
- Warnings when reaction conditions may increase risk of star activity or poor digestion.
Recommended workflow for a successful double digest
1) Confirm enzyme compatibility first
Before mixing anything, verify that both enzymes are active in the same buffer and at the same temperature. If not, plan a sequential digest. The calculator gives volume math, but enzyme compatibility still needs to be checked against your supplier data.
2) Keep enzyme and glycerol load reasonable
A frequent source of trouble is adding too much enzyme stock, which also adds glycerol. Higher glycerol and high enzyme percentages can increase star activity. If warnings appear, increase total reaction volume or use more concentrated DNA/enzyme stocks.
3) Use enough units for the DNA amount
For many routine digests, 10 U per µg DNA per enzyme is a good baseline. Difficult templates, methylation-sensitive sites, or short incubations may require optimization.
4) Incubate and heat-inactivate as appropriate
Typical incubations are 15-60 minutes at the recommended temperature with modern high-fidelity enzymes, but always follow the specific product protocol. Not all enzymes can be heat-inactivated.
Troubleshooting guide
- No cutting or partial cutting: verify buffer, temperature, and site accessibility; check if DNA prep contains inhibitors.
- Unexpected bands: confirm plasmid map orientation and expected fragment sizes; rule out mixed colony prep.
- Smearing: reduce incubation time, avoid over-digestion, and minimize freeze-thaw stress on DNA.
- Ligation fails after digest: ensure full inactivation/cleanup and consider phosphatase treatment of vector backbone.
Example planning scenario
If you digest 1 µg DNA at 100 ng/µL in a 50 µL reaction with two enzymes at 20 U/µL and target 10 U/µg each, the calculator returns:
- DNA: 10.00 µL
- 10X buffer: 5.00 µL
- Enzyme 1: 0.50 µL
- Enzyme 2: 0.50 µL
- Water: 34.00 µL
This setup keeps both total enzyme volume and glycerol comfortably low.
Final notes
This calculator is for educational and planning use. For production workflows, always cross-check with the latest enzyme datasheets and your lab's validated SOPs.