answered 9/22/2009 How Much Water In Litres Is Contained In 3 Metres Of 15mm Copper Tube? Internal diameter of 15mm pipe is 12,8mm, formula is pi x radius squared x length of pipe . I.e. 0.64cm x 0.64cm x pi (3.142) x 300cm = 386 cc. Note: 1 cc = 1 ml (approx.) . Therefore volume in pipe is 386 mls = 0.386 litres.