It can be calculated (but don't ask
). Just to give you a
rough idea, there are standard charts for head loss per 100ft of copper pipe. The numbers will
not be the same for silicon/tygon tubing, but it will at least give you an idea of the order of magnitude head loss
There are a fair number of plumbing related web sites that have those charts, you just have to find one that has 3/8"
I.D pipe on it, lol. You can find some numbers on the affect of 90 degree bends as well (note the radius of the bend has a significant impact). The affect on your flow rate will depend upon how
your pump reacts to the increased head. You'll have to get a curve for the pump your using to see that.
If you wanted to see for your pump approximately what the difference is fairly easily - get you some scrap or cheap vinyl tubing (say a few feet of each size at the hardware store), put water in something that can hold say 5 or 10 gallons, put your test hose on the pump output, prime the system, then measure how long it takes to pump 4 or 9 gallons (the larger the amount of water you use, the less affect your timing inaccuracy will have on it). Then multiply the length of tubing you used by the length in your system.