Hi Martin
Assuming like in your example that the string only has spaces, commas and digits, try in B1:
=LEN(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1," ",""),",",""),"0",""))
<table style="border-color: rgb(204, 204, 204); border-width: 2px; background: rgb(255, 255, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; border-collapse: collapse; font-family: Arial,Arial; font-size: 10pt;" border="1" cellpadding="1"><tbody><tr><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;"> </th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; text-align: center;">A</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; text-align: center;" width="30">B</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; text-align: center;" width="30">C</th></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; text-align: center;">1</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: left;">1, 0, 3, 7, 2</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">4</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;"> </td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; text-align: center;">2</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: left;">1, 4, 5, 0,4,0, 5</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">5</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;"> </td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; text-align: center;">3</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;"> </td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;"> </td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;"> </td></tr><tr><td colspan="4" style="background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; padding-left: 1em;"> [Book1]Sheet2</td></tr></tbody></table>