php help: convert a , into a .

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Hi,
how can I convert an input: $num1 = $_POST['num1'];
Say someone enters 1,5 and I want this to convert to 1.5

How can I do this?

Thanks for your time

Gr8t

Thank you

$conv = str_replace(",", ".", $num1);
echo($conv); // to test it out

works perfectly, thanks a million