A 318 sits just above the average for most graduate fields. That makes it workable, and it makes the next few points unusually cheap.
You are slightly ahead of the field averages and well short of the ceiling. That combination makes a 318 one of the more improvable scores on the scale, if you have a reason to improve it.
Above average and workable. A 318 clears the reported average in 8 of the 8 fields ETS tracks.
Adding your two section scores together is something you do, not something ETS does. There is no official meaning attached to 318 as a single figure, which is why two people holding it can be in very different positions.
Run through the ways of assembling a 318 and the section percentiles swing from the 19th to the 99th. A committee sees where you actually landed in that swing; the total does not.
Take the even split, 159 and 159. Same number twice, 80th percentile on one section and 47th on the other. Anyone comparing their two scaled scores directly is comparing different rulers.
Every field ETS reports sits below a 318 — the highest of them, Physical Sciences, averages 314. There is no discipline where this total reads as weak.
Read them as a temperature check. They place your score inside a discipline; they say nothing about a particular department's expectations, which vary far more than the field mean suggests.
Do not study "the GRE" from a 318. Study the section that is costing you, which for most people is not the one they find least pleasant.
On a balanced split your Quant score is the lower percentile of the two, which usually makes it the cheaper place to buy points: the distribution is thinner there, so each scaled point moves you past more people.
Practically: quant drills or verbal drills depending on which half you picked, a two-month plan so it has an end date, and full timed tests to check it is holding under pressure.
A total hides the two numbers programmes read. Run your Verbal and Quant through the GRE percentile calculator to see the published percentile for each, then compare those against your field rather than comparing 318 against a rule of thumb.
Check your section percentilesThis is a real decision rather than an obvious one. A 318 is close enough to the field averages that a few points changes which side of them you are on, and close enough that those points are gettable.
Look up your field's average Verbal and Quant, compare them against your two scores rather than your total, and go again only if one is clearly behind.
Decide which section to push before booking anything. Adding points to the section your field actually reads is worth several times as much as adding them to the other one.
The honest answer is that a total percentile does not exist. Your two halves do: 80th and 47th respectively on a balanced 318.
Yes — it is above the reported average in all 8 fields ETS tracks, so no discipline reads it as weak.
Many combinations, and they are not equivalent: 148V/170Q and 170V/148Q both total 318 but read very differently.
Only with a named target. Compare each section against your field's average rather than the total, and go again if one is clearly behind.