Example Data Table
| Input |
Example value |
Meaning |
| Total reaction volume |
50 µL |
Final digest tube volume. |
| DNA amount |
1000 ng |
One microgram of target DNA. |
| DNA concentration |
100 ng/µL |
Gives 10 µL DNA volume. |
| Enzyme stocks |
20 U/µL each |
Used to estimate enzyme volume. |
| Buffer |
10X to 1X |
Uses 5 µL in a 50 µL reaction. |
Formula Used
DNA volume: DNA volume = DNA amount ÷ DNA concentration.
DNA in micrograms: DNA µg = DNA ng ÷ 1000.
Time factor: Time factor = maximum of 1 and 60 ÷ incubation minutes.
Activity factor: Activity factor = 100 ÷ enzyme activity percent.
Required units: Units = DNA µg × units per µg × time factor × activity factor.
Enzyme volume: Enzyme volume = required units ÷ enzyme stock concentration.
Buffer volume: Buffer volume = final volume × desired buffer strength ÷ stock buffer strength.
Water volume: Water = total volume − DNA − buffer − enzymes − additive.
Glycerol estimate: Final glycerol % = total enzyme volume × stock glycerol % ÷ final volume.
How To Use This Calculator
- Enter the final reaction volume for your double digest.
- Add DNA amount and DNA concentration.
- Enter both enzyme names and stock unit concentrations.
- Enter the recommended units per microgram of DNA.
- Choose buffer stock strength and desired final strength.
- Add activity percentages for both enzymes in the selected buffer.
- Include an optional additive only when your protocol needs it.
- Press the calculate button and review the result above the form.
- Download CSV or PDF for your lab record.
NEB Double Digest Planning Guide
A double digest uses two restriction enzymes in one tube. The goal is simple. You want both enzymes active in the same buffer. You also want enough units, enough DNA, and enough water to reach the final volume. This calculator turns those choices into a practical reaction layout.
Why Reaction Balance Matters
Restriction enzymes are supplied in storage liquid that usually contains glycerol. Too much enzyme stock can raise glycerol levels. High glycerol may increase star activity. That means an enzyme may cut at unwanted sites. The tool checks enzyme volume percent and estimated glycerol percent. These checks help you keep the mix controlled.
Buffer Compatibility
Many double digests work well when both enzymes show strong activity in one buffer. Enter the activity percentage for each enzyme in your selected buffer. The lower value becomes the compatibility guide. Low activity does not always mean failure. It means you should consider more enzyme, longer incubation, or a sequential digest.
Using DNA Amount
The DNA volume comes from mass and concentration. Accurate DNA measurement is important. A weak concentration can consume much of the reaction volume. If the DNA volume is too high, the water value may become small or negative. In that case, concentrate the DNA or increase total reaction volume.
Interpreting Results
The result table lists DNA, buffer, enzymes, optional additive, and water. It also reports units, final glycerol, and practical warnings. Use the CSV export for spreadsheets. Use the PDF export for records. Always confirm enzyme notes, methylation sensitivity, temperature, and incubation rules from the supplier before preparing samples.
Good Lab Practice
Keep enzymes cold. Add them last. Mix gently. Spin briefly before incubation. Use nuclease free water and clean tubes. When working with valuable DNA, run a small test digest first. Review band sizes before scaling the reaction. Careful planning saves sample, time, and troubleshooting work.
When To Change The Plan
Change the plan when warnings appear. A negative water volume means the reaction is overfilled. A high enzyme percentage means the stocks dominate the tube. Low shared activity suggests a different buffer. A high DNA volume suggests cleanup or concentration. Small changes often improve digestion reliability and cleaner downstream ligation results later.
FAQs
What is a double digest?
A double digest uses two restriction enzymes in one reaction. It can save time and sample. Both enzymes must work well in the same buffer and temperature.
Can this calculator replace supplier instructions?
No. It is a planning tool. Always confirm enzyme activity, buffer choice, temperature, methylation notes, and incubation guidance from the official enzyme documentation.
Why is glycerol percentage important?
Restriction enzymes often arrive in glycerol storage solution. Too much glycerol in the final tube may raise star activity risk and reduce digest specificity.
What does buffer compatibility mean?
It estimates how well both enzymes perform in one selected buffer. The calculator uses the lower activity value as the compatibility guide.
What should I do with negative water volume?
Negative water means the entered components exceed the final volume. Increase reaction volume, reduce DNA volume, or use more concentrated stocks.
Why include incubation time?
Shorter incubation may need more enzyme units. The calculator increases estimated units when incubation is below one hour.
Can I add BSA or another additive?
Yes. Use the optional additive fields. Enter stock strength and desired final strength. Leave it unchecked when your protocol does not require it.
Why export CSV and PDF?
CSV helps with spreadsheets. PDF helps with bench records. Both exports make the planned digest easier to save, share, or review.