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From very improvisationsl origins, multiple marks of limpets were developed by the British. Hopefully, these links will get you started:

An overview. Ignore the clam limpet. It was a small device for blowing up cars on land:

http://michaelhiske.de/Allierte/USA/USNBD/GBR/LandminesUK/Section04/Page081.htm

From the above link, I get this:

"The explosive container of the Mk III Limpet is a separate unit which can be de-tached from the magnet ring so that the device can be used without magnets if desired. This container filled weighs about 4¼ lbs. The magnet ring weighs 5¼ lbs., bringing the total weight of the device to 9½ lbs."

This is the largest one I came across, thus the most direct answer I can provide for you.

Two views of a common late war type with a smaller weight explosive charge:

https://www.relics.org.uk/limpet-mine-worldwar2-british

https://www.iwm.org.uk/collections/item/object/30102144

A wiki discussion page for the subject:

https://www.imfdb.org/wiki/Talk:Limpet_Mine

This is a forum of dedicated enthusiasts. You might want to join it and ask them:

https://www.bocn.co.uk/threads/british-limpet-mine.74668/

More generic general info on multiple related devices:

https://ww2data.blogspot.com/2017/04/british-explosive-ordnance-army-and.html?m=1

HTH some