Camille / Kelsey Grammer's Malibu Mansion for Sale -- $17.9 MILLION

8/28 -- Camille tells TMZ ... the property actually contains roughly 17,000 square feet of living space.

She explains ... the guest house alone is about 8,000 sq. feet ... and the main house is somewhere between 8,000 and 9,000 ... she's not sure about the exact measurements.

Wanna own the home where Camille Grammer lived on "Real Housewives"? Got $17.9 million to spare?

The GIGANTICALLY ENORMOUS Malibu pad -- which is owned by Kelsey and Camile -- has officially hit the market ... for more than 3-TIMES what they paid for it back in 1998.

The place is sick -- 6,645-square-feet, 4 bedrooms, 6 bathrooms, a kitchen personally designed by Wolfgang Puck, library, ocean views and a 12-seat home theater.

And there's more ... the property includes a 9-stall barn, lighted tennis court and huge guest house with a roof deck.

According to reports, Camille and Kelsey bought the place together for $4.5 mil.

Sources tell TMZ ... Camile and Kelsey struck a deal in their divorce -- to sell 3 of their properties, including Malibu, and split the proceeds. As for the other 2 estates that are on the market ... one is in Beverly Hills (listed for $18 million) and the other is in Beaver Creek, Colorado (listed at $7 million).