Darren Sharper -- He'll Serve 9 Years NOT 20 for Louisiana Rapes

Darren Sharper will be sentenced to 20 years in Louisiana for raping 3 women, but he will only serve 9 of those years behind bars ... TMZ Sports has learned.

Media reports saying Sharper will serve 20 years for the Louisiana rapes are incorrect.

Law enforcement sources tell us ... Louisiana prosecutors have agreed in the plea deal, after serving 9 years Sharper will get credit for the remaining 11 while free on parole and probation.

We're told the Louisiana sentence will be served concurrently with sentences in California, Nevada and Arizona. All 4 states require Sharper behind bars for 9 years or less, so 9 is the operative number.