I think GCN's response is quite clear - 215 kg.
However, the only way you will really know is to carry out a calibration refuel with the airframe in the attitude for your required answer. Meaning that if you want the data for cruise situation, then the airframe must be levelled at that attitude before the calibration starts.
Fill the tank, litre by litre and observe the point at which the fuel flows into the supply tanks through the ports. This will provide you the answer.
Or off course you could do a calibrated defuel at the required attitude and take out the fuel from the suppy tanks until no more fuel can be exracted and see what's left in the tank.