The Ratio = Average Tech / [1+(Total % penalty)/100]. ​

Year 5-15: Starting World

Year 16-50: Expansion!

Year 51-100: Expansion II:

Year 101-150

Year 151-200

Year 200+

Many walls of text have been posted about what the minimum size planets should be before you choose to colonize them, the potential advantage of avoiding settlement so that you can avoid the dreaded Research Malus, and so on. So I thought I'd post a *brief* guide to the benchmarks I've experienced so far in *single player* and give a little advice. (You MP folks that probably have to do nothing but build Corvettes for the first 50 years ... not sure this applies to you.)Before I start -- it goes without saying that there are a ton of reasons to settle planets -- moar minerals, moar fleet size, moar territory -- but for the moment we're just going to focus on The Science.The Key Calculation that serves the basis for all of this is what I will call The Ratio.Your Total % penalty is easily found by going to the 'choose research' screen and hovering over the tech cost, and is +10% for each planet beyond the first, and +1% for each pop beyond the 10th, e.g.:In this game, the Ratio is about 71 for Physics (872/12.2 = 71) and still slowly climbing -- but it's a Peaceful, Happy empire that's focused on settling large planets.Your Ratio is going to be split up about three ways -- 1/3rd will be the 5 research points (RPs) per tech that you start with, 4 RPs (-ish) for research stations you hopefully have, and 4 RPs (-ish) for research labs on your home planet. This puts your Ratio at 13. Your goal, of course, is to drive this up, up, UP throughout the game.Luckily, this is easy. With a Ratio of 13, and a +10% penalty per planet settled, and +1% per pop, you'll get a research boost if you can exceed just a couple RPs per tech per planet -- early on, at least. If you want a boost, settling any planet that gives you a total of +6 across all the different techs just in research stations will get you an advantage, and that's before you build a single lab.However, this does mean that if you settle a big-ass planet in your system and it *doesn't* expand your borders, you'll take an immediate 11% hit that will slowly get worse without labs. Not the end of the world, but it shows that settling outside your borders is a much better idea.Your Ratio is hopefully going up at this point, or at least isn't crashing. Hopefully by now you've got a second science ship and are looking all over the damned place for a spot to drop a Frontier Outpost -- there are always a tiny number of clusters of 2-4 very science-rich planets at various points on the map, and these are worth targeting with outposts (as they often don't have planets you can actually settle on).If you're in Early Conquering mode, you might drive your Ratio *up* even with having some lousy early planets, just because of border expansion means access to a bunch more research stations.At this point, there's enough planets of size 18+ and/or other concerns (minerals, building a fleet, etc.) that we'll skip ahead to where the question of when-to-settle becomes more interesting ...Your Ratio is a climbin' to the 25-50 spot, but you warmongers will notice that it's leveling off. At this point, 18+ size planets full of research labs are driving your total Science, not research stations -- at least, that's what's going on with those peaceful chumps who are nurturing their big planets until they're maxed out before turning them over to sector AI.Let's assume that it's fully within your system, and we'll also assume a Happiness of 50% (probably conservative) -- so, worst-case-scenario x2. But we'll ignore the hit you'll take while you're waiting for the pop to get big enough to support all those labs you'll have on it.To maintain a Ratio of 30, you'll need:-- For a planet of size 10, 6 RP per tech type, or 18 total.-- For a planet of size 15, 7.5 RP per tech type, or ~22 total.-- For a planet of size 20, 9 RP per tech type, or 27 total.For a planet of size 20, if you have half the spots with mere level-2 labs, you're getting 10 x 5 RP = 50 RPs total, not including any free research on the planet. It's a good deal.For a planet of size 15, if you have 7 spots with mere level-2 labs, you're getting 7 x 5 RP = 35 RPs total, not including any free research on the planet. It's a good deal.For a planet of size 10, if you have 5 spots with mere level-2 labs, you're getting 5 x 5 RP = 25 RP total, not including any free research on the planet. STILL a good deal ... in fact, with a little free research, you're breaking even with just 5 basic labs.Keep those numbers in mind, though, for future calculations ...At this point, your ratio is probably between 40 and 60, depending on whether you're warring a bunch or you're going with peaceful expansion. Unless your borders are expanding with a new settle,Still obviously a good deal for a size 20 planet, and probably okay for size 15 if you can squeeze on a couple more labs and make sure you max them out. Smaller than that, though -- going to be a net minus, unless you're at 90% happiness or somesuch. What the happiness bonus is depends on the patch, it seems, and of course you'll get bonuses for governor and potentially edicts -- so you may want to increase your projected research RPs by 10-20% when doing the maths.Your Ratio's either plateaued at 40-50 (if you're a warmonger with a bunch of planets full of grumpy aliens and slaves getting managed by idiot sector AIs) but could be as high as 80 (if you're expanding to only large planets and maxing them out as much as possible before turning them over to sectors).At a Ratio of 80, you're technically not gaining at ALL with even large planet sizes using my guidelines but we both know that if your Ratio is 80, it's because you're running with Happiness of 75+, using Intelligent races, have some Edicts in the background or Sector govs who are intellectuals, and so on and so forth. Still, very unlikely at this point that any planet of size 16 or lower is going to help you out unless you have the resources to put a lab on every single spot. And do you really want to spend thousands of minerals just to be able to increase your Ratio by a fraction of a point ... eventually?You're still playing?-----------Early on, if you want to increase your Ratio, expanding your borders is much more important than worrying about planet size. It's worth it to settle a size-10 planet if it comes with a border bump. Also, consider Frontier Outposts around very science-rich spots.In mid-game, if your a warmonger, you probably aren't thinking too much about settling, but it's doubtful that you'll get burned by settling a small planet or two. if you're Peaceful Magoo, focus on 16+ if you're thinking long-term, or 12+ if that settle is going to give you a strong border expansion. Smaller than that and you'll end up penalized, EVEN after building level-X labs.In late-game, if all you're thinking about is maxing out science, you're probably not going to benefit from settling anything smaller than size 16, even after you max out research labs on most planet spots -- though mileage may vary if you're just a damned Happy Guy.TL;DR: Everything you've read about avoiding settling small planets is mostly correct, but you should probably worry less about it than you have.