Percentage is always the mass of a substance (expressed as in grams) contained in 100 ml of solution. Therefore you don't need a formula, nor a calculation, just weigth for example 1.5 grams of agarose, put it in 100 ml desired buffer TAE or TBE, let it swell and then boil to homogeneity.

Whether choosing the right percentage of agarose for your application, well, that depends on the application. Precisely if it's nucleic acid or protein to resolve, which resolution you need for your bands, etc. Let us know if this is the case.

There is no specific formula. You can Google "agarose gel guidelines" and you can find tables of suggested concentrations, such as at:

http://www.agctsequencing.com/NLGelPercent.asp

It is generally said that lesser the size of amplicons, more the agarose concentration should be to visualise the bands. I just wanted to know what is the limit of agarose gel to show the DNA bands. In what condition should i shift to a SDS-PAGE instead of agarose.

Firstly, SDS-PAGE is generally for proteins and DNA/RNA acrylamide gels are made with a different ratio of acrylamide to bis-acrylamide and contain different appropriate buffers/additives. Acrylamide gels are usually used in situations where you need superior resolution--to detect the differences between fragments which differ by less than 10-20 nucleotides say. [Although there are some "high-resolution" agaroses that will also perform similarly.] If you only want to see whether you have a product or not (+/-), then you can run an ordinary agarose gel, and the actual percent agarose that you use is not very critical. If you have never used agarose, be aware that you should purchase one that has been qualified for nucleic acid separation. Some low grade agaroses have other applications and will not work for DNA/RNA gels!

Thank you David Barker. Can you just tell me what EEO(electro endo-osmosis) value that is mentioned in the agarose product, signifies in terms of using it for dna electrophoresis.

"Low" is better. "Medium" may work. "High" is associated with band smearing, which you want to avoid.

Veera, sorry I am late!

Find attached two tables to guide agarose selection for submarine electrophoresis. In my experience, 0.8-1.2 for DNA/RNA inspection or "big gel" running of digested DNA. For PCR products, 2% suits quite well to a range of sizes. You can use until 3% of common molecular grade agarose (more than that the gel gets very frail) if the size to be separated is between 100-200 bp and you need a better discrimination power. Less than 100 bp, I would suggest using non-denaturating 8% PAGE 39:1 or 29:1 acrilamide /bis (and not SDS-PAGE), and also for discriminating a few bp (as for instance in microsatellite analysis). Do not use low melting agarose for discriminating purposes (you can use it for isolating a big fragment of for "in gel" cloning).

Hope to have helped you!

See also this document! Good luck.

Yes Veera, here is the formula:

Agarose (g) = Percent * Volume.

For example, to calculate the mass of agarose required to prepare 0.7% agarose gel in 40ml TAE,

Agarose (g) = (0.7/100) x 40

Agarose (g) = 0.007 x 40

                       = 0.28g.

Therefore, to prepare 0.7% agarose gel, measure out 0.28g of agarose and dissolve in 40ml TAE buffer.

Hope this really helps you. 

Regards, from me UC.

Veera Manikandan R

Maybe this link can help you to understand more about this issue;

https://worldwide.promega.com/resources/pubhub/enotes/how-do-i-determine-the-concentration-yield-and-purity-of-a-dna-sample/

https://assets.fishersci.com/TFS-Assets/LSG/manuals/MAN0012614_Gen_Recommend_DNA_Electrophoresis_UG.pdf

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