The coronavirus pandemic has sent panicked shoppers across Europe into a toilet-paper buying frenzy. But how much do you really need? And what to do if the unthinkable happens and you run out?

A German online calculator is here to help.

At www.blitzrechner.de/toilettenpapier, curious users can work out how long their stockpile will last.

Just type in how many rolls you have and your individual "usage behaviour" and the calculator will tell you for how many days you'll be covered.

For true aficionados, there is an expert mode where you can add the length of your quarantine and your average number of sheets per wipe.

Generally speaking, people tend to wildly overestimate their TP needs, the website says.

"Many people use more toilet paper than needed. For a 'number one', one or two sheets should suffice," it adds.

The website also offers some suggested alternatives to toilet paper should the supermarket shelves be bare.

Washcloths, strips of old rags and even a quick shower are all good options. But be careful not to flush kitchen roll as it could clog up the toilet.

Germany, like many European countries, has seen demand for toilet paper spiral since the start of the outbreak.

Similar tongue-in-cheek stockpiling calculators have sprung up in other countries too, like the UK site Howmuchtoiletpaper.com.

Videos of scuffles in supermarkets have been circulating widely on social media -- one argument over toilet paper in a supermarket in Mannheim last week even ended in a fistfight that required police intervention.

Chancellor Angela Merkel set a better example when she was photographed doing her weekly shop last Friday with just one pack of toilet paper in her trolley -- and four bottles of wine.