Calculate insert mass and molar ratio, then turn DNA stock concentrations into a practical ligation pipetting plan. Learn more
How do I calculate DNA insert for a ligation reaction?
Enter the vector length, vector mass, insert length, desired insert:vector molar ratio, and measured stock concentrations. The calculator returns the required insert mass, compares common ratios, and calculates vector and insert volumes for the reaction. Turn off Calculate stock volumes when concentrations are not available.
For a 4,000 bp vector, 50 ng vector mass, 1,000 bp insert, and a 3:1 insert:vector ratio:
Vector: 4,000 bp, 50 ng
Insert: 1,000 bp
Target ratio: 3:1
Required insert mass: 37.5 ng
Vector amount: 18.939 fmol
Insert amount: 56.818 fmolFor a 3,000 bp vector at 50 ng and a 1,000 bp insert at 3:1, with vector stock at 25 ng/µL and insert stock at 10 ng/µL:
Vector stock per reaction: 2 µL
Insert stock per reaction: 5 µL
Total DNA concentration in a 20 µL reaction: 5 ng/µL
Volume remaining for buffer, ligase, and water: 13 µLWhat do vector, insert, and molar ratio mean?
The vector is the DNA molecule that will carry the new sequence. It is usually a linearized plasmid. The insert is the DNA fragment being joined into that vector.
A 3:1 insert:vector molar ratio means three insert molecules for every vector molecule. It does not mean three times as many nanograms of insert. A shorter DNA fragment weighs less per molecule, so fragment lengths are required to convert the molar ratio into masses.
Input and settings
This calculator is for linear double-stranded DNA. It does not require a sequence or file.
| Setting | Accepted values | Default | What it controls |
|---|---|---|---|
Vector length | Number greater than 0 | 3000 | Length of the linearized vector. |
Vector length unit | bp or kb | bp | Unit for the vector length. |
Vector DNA mass | Number greater than 0 | 50 | Vector mass added to each reaction. |
Vector mass unit | ng or µg | ng | Unit for the vector mass. |
Insert length | Number greater than 0 | 1000 | Length of the insert fragment. |
Insert length unit | bp or kb | bp | Unit for the insert length. |
Insert:vector molar ratio | 1:1, 2:1, 3:1, 5:1, 7:1, 10:1, or Custom ratio | 3:1 | Number of insert molecules per vector molecule. |
Custom insert:vector ratio | 0.01 to 100 | 3 | Shown only when Custom ratio is selected. |
Calculate stock volumes | On or off | On | Enables the pipetting plan. |
Vector stock concentration (ng/µL) | Number greater than 0 | 25 | Measured vector stock concentration. Shown when stock volumes are enabled. |
Insert stock concentration (ng/µL) | Number greater than 0 | 10 | Measured insert stock concentration. Shown when stock volumes are enabled. |
Reaction volume (µL) | Number greater than 0 | 20 | Final volume including DNA, buffer, ligase, and water. |
Number of identical reactions | Whole number from 1 to 1000 | 1 | Scales total DNA stock requirements. It does not add excess volume. |
Minimum pipetting volume (µL) | Number greater than 0 | 0.5 | Volumes below this threshold receive a dilution suggestion. |
Results
| Result | How to use it |
|---|---|
| Required insert mass | The insert DNA mass for the selected molar ratio. |
| Vector and insert amount | Estimated molecule amounts in fmol or pmol. |
| Ratio comparison | Insert mass and molar amount for common ratios from 1:1 through 10:1. |
| Pipetting plan | Vector and insert stock volumes per reaction and across identical reactions. |
| Total DNA concentration | Combined vector and insert mass divided by the final reaction volume. |
| Remaining reaction volume | Space left for buffer, ligase, and water after adding the DNA stocks. This is not the water volume by itself. |
| Dilution suggestion | A target stock concentration that makes the selected minimum volume pipettable. |
| Checks | Protocol guidance for unusual ratios, DNA concentration, small volumes, or DNA stocks that overfill the reaction. |
| Run log | A concise record of the inputs, calculated amounts, pipetting plan, and warnings. |
The Result tab opens with the required insert mass, the selected ratio, a compact ratio comparison, and a pipetting plan when stock concentrations are provided. Data contains the complete comparison table. Files provides the ratio table as CSV, the complete calculation as JSON, and the downloadable run log. The Logs tab appears last and shows the same concise run record.
Ligation calculation formula
The required insert mass is:
For molar estimates, the calculator uses an average double-stranded DNA molecular mass of 660 g/mol per base pair:
The 660 value is an average. The insert mass ratio itself depends on relative fragment lengths, so the average molecular mass cancels when both fragments are double-stranded DNA.
How should I choose an insert:vector ratio?
A 3:1 insert:vector ratio is a common starting point for a single insert. Testing more than one ratio can be useful when the ligation is difficult. The result table always includes 1:1, 2:1, 3:1, 5:1, 7:1, and 10:1 so the amounts can be compared without repeating the calculation.
Ratios outside 1:1 to 10:1 receive a warning because they are outside a commonly recommended range for single-insert T4 DNA ligations. Some short adaptors use higher ratios. Follow the instructions for the ligase, vector system, and end type in use.
Does this calculate ligation efficiency?
No. The calculator sets the vector and insert stoichiometry. It cannot predict a ligation efficiency percentage from DNA masses alone.
Actual ligation success also depends on compatible ends, 5′ phosphorylation, vector dephosphorylation, DNA purity, ligase activity, buffer composition, ATP, incubation conditions, transformation efficiency, and construct biology. The concentration and pipetting checks identify setup issues, not experimental success probabilities.
Which DNA tool should I use?
| Goal | Tool |
|---|---|
| Calculate insert mass and pipetting volumes for ligation | DNA ligation calculator |
| Turn plain DNA sequence text into a FASTA file | TXT to FASTA converter |
| Calculate sequence composition | GC content calculator |
| Generate the opposite DNA strand | Reverse complement generator |
| Check short DNA oligo properties and structures | Oligo analyzer |
| Design PCR primers | Primer3 |
FAQ
Is this the NEB ligation calculator?
No. This is an independent ProteinIQ calculator that uses the same standard insert:vector mass equation. It additionally calculates molar amounts, stock volumes, reaction concentration, ratio comparisons, and dilution suggestions. ProteinIQ is not affiliated with New England Biolabs.
Can I use this as a T4 DNA ligase calculator?
Yes, for planning the vector and insert DNA amounts in a standard T4 DNA ligation. Use the buffer, ligase amount, temperature, and incubation time specified by the exact T4 DNA ligase product.
Why is the insert mass not three times the vector mass for a 3:1 ratio?
The ratio counts molecules, not mass. A 1,000 bp insert has one quarter the mass per molecule of a 4,000 bp vector, so a 3:1 molar ratio requires 37.5 ng insert for 50 ng vector.
Should the insert be shorter than the vector?
Not necessarily. The formula works when the insert is shorter or longer than the vector. Whether a construct is practical depends on the cloning method, vector capacity, transformation system, and protocol.
Does the remaining reaction volume equal the water volume?
No. It is the volume left after vector and insert stocks. Buffer and ligase must be subtracted before calculating how much water to add.
Can this perform in silico ligation of DNA sequences?
No. In silico ligation joins and validates sequence ends. This calculator plans physical DNA amounts and volumes for a ligation reaction; it does not inspect restriction sites, overhang compatibility, or assembled sequence.
