neb digestion calculator

How this NEB digestion calculator helps

Restriction digests are simple in principle, but tiny volume errors can easily cause incomplete cutting, star activity, or failed cloning. This NEB digestion calculator gives you a fast, practical starting point for planning reaction components from real lab inputs: DNA mass, stock concentration, reaction volume, and enzyme potency.

Instead of manually converting ng to µg and then units to enzyme volume each time, you can enter your values once and get a clear recipe for water, buffer, DNA, and enzyme(s). It also flags common issues like high enzyme percentage, excessive glycerol, or pipetting volumes that are too small to handle accurately.

Core assumptions behind the calculator

• Buffer: Uses 10X buffer at 1X final concentration (buffer volume = total volume / 10).
• Enzyme stock: Assumes restriction enzymes are in ~50% glycerol.
• Unit definition: 1 unit typically digests 1 µg of substrate DNA in 1 hour under optimal conditions.
• Planning approach: You choose units per µg DNA, and the calculator converts that into required enzyme volume.

These are standard planning assumptions, but always confirm details in the specific NEB product protocol and compatibility chart for your exact enzyme pair and substrate.

Input guide

1) DNA amount (ng)

This is the total mass of DNA you want to digest, not the concentration. For routine plasmid digests, 200 ng to 2 µg is common depending on downstream needs.

2) DNA stock concentration (ng/µL)

Used to compute the DNA volume added to the tube. Example: 1000 ng DNA from a 100 ng/µL stock means 10 µL DNA volume.

3) Total reaction volume (µL)

Common reaction sizes are 20 µL or 50 µL. If enzyme volume becomes too high, increasing total reaction volume can reduce the relative amount of glycerol and help avoid star activity.

4) Enzyme concentration (U/µL)

Taken directly from the vial label or product sheet. Different enzymes can have different concentrations, so check each one.

5) Units per µg DNA

This determines how aggressively you digest your DNA. A common conservative choice is 5–10 U/µg DNA per enzyme for robust cutting, though exact recommendations vary by enzyme, DNA type, and incubation conditions.

Single digest vs. double digest

For a single digest, only Enzyme A is included. For a double digest, enable Enzyme B and provide its concentration and units-per-µg target. The calculator then returns both enzyme volumes plus updated water volume.

In double digests, the limiting factor is often buffer compatibility and enzyme performance in the same conditions. If activity is poor for one enzyme in a shared buffer, sequential digestion may be more reliable than simultaneous incubation.

What the warnings mean

• Total enzyme volume > 10% of reaction: often discouraged because excess storage components can increase off-target activity.
• Final glycerol > 5%: can raise risk of star activity for some enzymes.
• Very small enzyme volume (< 0.5 µL): hard to pipette accurately; dilute enzyme or scale reaction.
• Negative water volume: impossible setup; reduce DNA volume or enzyme demand, or increase reaction size.

Best-practice digestion workflow

1. Set your desired DNA mass and reaction scale.
2. Use this calculator to generate an initial mix.
3. Check enzyme pair compatibility in the official NEB tools/resources.
4. Assemble on ice: water, buffer, DNA, then enzyme last.
5. Incubate at recommended temperature and time.
6. Heat-inactivate or clean up as required before ligation, PCR, or gel purification.

Troubleshooting incomplete digestion

Problem: undigested band persists

• Increase units per µg DNA.
• Extend incubation time.
• Verify buffer and temperature are correct for both enzymes.
• Check methylation sensitivity and DNA source.

Problem: unexpected band pattern

• Consider star activity from high glycerol, long incubation, or high enzyme load.
• Confirm plasmid map and expected fragment sizes.
• Run control digest with a known substrate.

Final note

This calculator is designed for quick planning and error reduction, not to replace enzyme-specific protocols. Use it as a practical setup assistant, then validate with manufacturer guidance and your lab’s validated SOPs. If you do this consistently, your cloning workflow becomes faster, cleaner, and much more reproducible.