How to use
- Enter the volume of one gel in mL and the target percentage. Percentage here is weight per volume, so 1% means 1 g of agarose in 100 mL of buffer.
- Casting more than one gel? Raise the count — volume and mass scale together.
- Pick the running buffer stock you keep. 50× TAE, 10× TBE and 5× TBE are set up; for anything else enter the fold yourself.
- Enter the fold of your stain stock and its volume appears too. Stain comes out of the water rather than on top of it, so the total stays the volume you asked for.
- Enter the fragment size in bp and the table below marks every percentage that resolves it.
Formula and practical notes
An agarose gel sieves DNA by pore size. More agarose means tighter pores and better separation of small fragments; less agarose opens the pores for large ones. That is why “what percentage do I need” is answered by a table, not by a formula.
The arithmetic
Four lines, and total volume is the volume of one gel times the number of gels.
- Agarose (g)
- target % ÷ 100 × total volume (mL)
- Buffer stock (mL)
- total volume ÷ stock fold
- Stain (μL)
- total volume ÷ stain fold × 1000
- Water (mL)
- total volume − buffer stock − stain
Practical notes
- Ethidium bromide (EtBr) is a suspected mutagen. Wear gloves, and treat the gel, the running buffer, the comb and the tray as contaminated. Casting it into the gel is convenient but contaminates the tank and slows linear DNA by about 15%; staining after the run uses less and keeps the tank clean.
- The concentration usually quoted for EtBr is a final 0.5 μg/mL. This calculator deliberately ships no stain as a default — enter the fold printed on the bottle you have.
- TAE has a lower buffering capacity than TBE and is exhausted sooner on a long run. TBE gives sharper bands and is particularly recommended below 1 kb, but its borate ions complex with sugars and make DNA harder to recover from the gel. For a gel you intend to cut and purify, TAE is the easier choice.
- Use ultrapure agarose. Polysaccharides, salts and proteins all distort migration, and the effect grows with the percentage.
- This is arithmetic on volumes and masses. What a gel actually resolves also depends on voltage, run time and the rig, so treat the table ranges as a starting point.
Frequently asked questions
It depends on the fragment you want to see. Enter the size in bp and the table marks the percentages that cover it. As a rough guide: large fragments above 10 kb at 0.5–0.7%, everyday PCR products between 0.5 and 10 kb at 1%, and anything under 1 kb at 1.5–2%.
Weight per volume (w/v). A 1% gel is 1 g of agarose in 100 mL of buffer, and that is what this calculator computes.
Yes. Changing the stock changes how much stock you measure, not how much agarose you weigh. Some benches keep TBE at 5× rather than 10×, so all three are offered; for any other fold, enter it yourself.
After the agarose has dissolved and cooled enough to hold, just before pouring. Adding it to boiling agarose degrades the stain and drives it off as vapour.
It answers with the nearest listed row and says that is what it did. Outside 0.3–2.0% it gives no range at all, rather than filling the gap with a guess.
References
Where the gel percentage / separation range table comes from. The mass, buffer and stain arithmetic is one multiplication and two divisions and is not cited.
- QIAGEN. Bench Guide — DNA analysis using analytical gels, table "Concentration of agarose used for separating fragments of different sizes". Read 2026-08-21.https://www.qiagen.com/us/knowledge-and-support/knowledge-hub/bench-guide/dna/analysing-dna/dna-analysis-using-analytical-gelsAll seven rows, 0.3 %–2.0 %, asterisks included, and the overall 0.1–25 kb range. Re-read from the rendered page on 2026-08-21; every row matched
Often used together
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