@PhilHibbs - Yes. You can put X cargo in then check your current max jump range via console nav points within range. Or you can use the Navigation tab on the Galaxy Map. Near the bottom is a little slider control that you can set to any point between fully laden or unladen and see your exact range that way.
@Vendraen - The guide was written specifically about commodity trade routes. I didn't want the title to be too lengthy, and I figured the executive summary would make it clear that I wasn't going to talk about rare routes. To me, rare trading is not challenging, because it's a matter of googling the best circuit for rare trading. Every point is fixed. Nothing is dynamic. Not to mention, FD recently nerfed rare trading. As @Armchair says, once you get a T6 (which comes pretty fast even if you've never traded a rare, ever, like myself) the numbers move quickly in favor of regular commodity trading if you can learn how to find the cash cow routes yielding >8000 cr/ton/hour.
To wrap your head around the process, start with the notion of "buy from HIGH supply and sell to HIGH demand or MEDIUM demand". In other words, look at the supply column at every station you land at. See a "HIGH" value there for any of the good commodities (Palladium, Gold, Progenitor Cells, etc.)? Then stop and look at the right side of the window for the list of "exported to" systems. Those are all prospects for a profitable sale. Pretty much all of those listed systems will be a HIGH or MED demand. Go investigate.
But now let's refine the technique and save yourself some time. Go into the Galaxy Map and on the View tab enable "Show trade routes". But NOT all of them! Click the Clear button. Then expand the category that contains the commodity you're interested in. For example: Metal > Palladium. Make sure only "Palladium" is checked. Now hover over every nearby system one or two jumps out from your current position and spend the 100 CR to buy the trade data for each system where available. You'll quickly see that the Palladium trade lines that appear correspond to that list of "Exported to" systems in the commodities window. What you're looking for is the ONE close by system that seems to have MULTIPLE lines converging on it. If a system has multiple converging lines from two or more other systems, it's _probably_ a HIGH demand system. So your best bet is to go check only the one or two systems from the "Exported to" list that seem to have multiple incoming trade lines for that commdoity. (By the way, conversely you'll notice that if you're currently at a HIGH supply station, you should see multiple lines originating from your current system to other systems.
Next nuance to master, to save time: When you find a HIGH supply item, check the "Buy" value against the "Galactic Average" value. If you can't buy it for AT LEAST 1000 cr below Galactic Average, stop right there and move on. You'll find that nearly every "cash cow" trade route features one or both commodities involved being purchased (by you) for at least 1000 cr below average, if not more. Most of of the huge variance from average is on the SUPPLY side, not the DEMAND side!
Got it so far? HIGH supply that you can purchase at more than 1000 cr below galactic average. That's where you start. If you don't see anything like that, move on to the next station. If you find something like that, then look at the "exported to" systems and spend the 1000cr or so it will take to populate all the current trade lines in the galaxy map to show you what's what in the area.
That's the basic "in-game" pattern to finding likely best candidates for a trade route. At least for one commodity, in one direction. The trick is to find a good target station that ALSO has a HIGH or MEDIUM supply commodity that is also in HIGH or MEDIUM demand at the current station from which you're shipping out (for example) Palladium. This is where the elbow grease and the pencil and paper and spreadsheets come in if you're doing it the hard way using only in-game tools. Why? Because in-game, the only way to see whether there's a good profit to be made on the return leg is to actually fly out to your top candidate stations and look for HIGH or MED supply commodities, then cross reference each one against the list you made of "Sell" prices from the first station. Yes, it's a PITA. A seriously time-consuming PITA, but some people enjoy that.
It's much easier to let a crowdsourced tool like Slopey's do the heavy lifting for you. Here, you don't care jack about HIGH or MED, etc. (In fact, some of the best profits can actually be had from MED supply to MED demand, but in both directions). When using a tool, all you care about is having it crunch the numbers to find the highest unit profit available in both directions. You're using the same general principles as in-game, but you're just using a souped-up calculator and a huge database of crowdsourced information from far more systems than you could possibly investigate for yourself.
Now, why do I say that some of the best profits can actually be had from MED supply to MED demand? This is my main beef with the in-game tools, which really serve to highlight only HIGH values on one end or the other. When you find a juicy HIGH supply item that is priced at something like 1400 below Galactic Average, one of the good target systems to export too will typically be buying it at roughly 200-350 above GA. For a nice juicy profit of 1600-1750 cr/ton. Sweet, right? But chances are VERY VERY CERTAIN that you won't find any decent trades from that other system back to the system you're making a sweet profit on. You might be lucky to find something you can schlep back at only 200 cr/ton, making your round trip worth something like 1800 cr/ton. If your round trip takes 15 minutes, that's only 7200 cr/ton/hour, which is below the "cash cow" benchmark.
However, if you can find a route where the profit in one direction is a modest 1150 cr/ton, and in the other direction it's 950 cr/ton, that's 8400 cr/ton/hour. These are actually fairly common to find, but you'll never find them in-game by keying in only on HIGH values to narrow down your list of candidates. Almost all runs like these will be based on commodities that are MED supply and MED demand at both ends.
Hope that helps!
