Shower room drain size???

Hello-

I am building a 8x11 shower room which will have two shower heads and one large soaking tub. I am wondering if (1) 2 inch drain will be sufficient or if I should go with a three inch or ???? Any help would be appreciated...

Chris

How deep is the curb around the shower room, are you on a septic tank or municipal sewer, what's the capacity of the soaking tub, what else is downstream from the drain?

drain

The amount of water in the soaking tub is immaterial. What is important is its drain and the gpm it will allow to exit the tub. The same with the showers. What is the gpm from the shower heads. Many multiple head showers, in fact the majority, get by with a conventional 2" drain.

The two showers will supply roughly 2-3 gpm, the tub drain will be 1.5 or 2 inch diameter. The curb will be 4-6 inches.

I know that the flow out of the tub will decrease as the water level decreases. I have written the equations but my calculus/differential equation solving is a bit rusty!

With 88 square feet of surface area and a 4 inch curb, the room can store a bit over 200 gallons.

I need to know what the max flow rate is for a 2 inch and 3 inch drain....

Any math whizes present?

Thanks,

Chris