In running there is a sweet spot around 15 - 25 miles a week that you get the most health benefit for your time...where is that for strength training?
3x a week
about 30-45 minutes a session
Bench Press 5x5
Bent Over Row 5x5
Overhead Press 5x5
One week do ABA (mon/wed/fri for example), next week do BAB.
To me that is pretty close to bare minimum requirements to grow at an effective and efficient pace.
Another routine example for bare minimums would be Jim Wendlers 5/3/1 (google)...
5/3/1 Bench Press
That is one of the most basic routines that is still an effective strength gainer.
Strength is relative to body-weight. The basics should be an ability to do calisthenics and climb, lift and bear moderate (realistic) weights...etc Imagine you need to be strong enough to climb trees and rock-faces, carry your child, take dinner home, move camp, sprint on occasion and push moderately heavy things off yourself. That's a basic level of human strength, a-la-"wild-human".
Perfection is entirely individual. Any philosophy or pursuit that encourages individuality has merit in that it frees people. Any that encourages shackles only has merit in that it shows you how wrong and desperate the human mind can get in its pursuit of truth.
I get blunter and more narcissistic by the day.
I'd apologize, but...
If you are lifting barbells, strstd.com is a great benchmark for you current strength levels.
This is a great description of barbell based strength levels (mark has a bodyweight specific one in the PBF pdf as well)
Within two years of consistent training on a decent routine, the average male should be able to progress to the following levels of strength (1RM):
Strength Goals: Intermediate
Bench press: body weight x 1.2
Chin-ups or pull-ups: body weight x 1.2 or 8 reps with body weight.
Squat: body weight x 1.6
Deadlift: body weight x 2
These numbers are for a raw (no straps, belt or knee wraps) single repetition.
The progress towards the intermediate strength goals should be fairly linear, meaning that there should be no plateaus that cannot be solved in an uncomplicated manner. By "consistent" training I do not mean never missing a training day, nor do I consider taking 2-3 months off from training consistent.
By "decent training routine", I mean "not doing blatantly stupid shit" (training 5-6 days/week, 20-25 sets for chest and arms, etc.). I do not mean optimal and flawless.
Strength Goals: Advanced
Under the exact same conditions as the previous example, 3 out of 4 of the following goals should be reached within five years, along with all of the strength goals listed under "intermediate":
Bench press: body weight x 1.5
Chin-ups or pull-ups: body weight x 1.5 or 15 reps with body weight.
Squat: body weight x 2
Deadlift: body weight x 2.5
Strength Goals: Highly Advanced
Under the exact same conditions, all of the following goals should be reached within ten years. Alternatively, 3 out of 4 should be reached, and one should be "Elite":
Bench press: body weight x 1.5, or x 1.8 (elite)
Chin-ups or pull-ups: body weight x 1.5 or 15 reps with body weight, or x 1.8 / 20 reps (elite)
Squat: body weight x 2, or x 2.4 (elite)
Deadlift: body weight x 2.5, or x 3 (elite)
"Elite" denotes one lift that is often ahead of the others. For example, people who are natural pullers (long arms) may very well hit a 3 x body weight deadlift before a 1.5 x body weight bench, and vice versa for the presser (short arms, stocky and barrel-chested) benching 1.8 x body weight but not being able to pull 2.5 x body weight in the deadlift.
The highly advanced strength goals falls in line with what could be considered the pinnacle of physique and strength development for most average and natural trainers. At this point, progress is very slow.
In my opinion, a good level of strength for a person not involved in strength sports is approximately at or near the point of the intermediate phase of lifting. The novice phase, the one prior to the intermediate phase, is when you can eat, sleep, lift, and make progress every time you do it. When you're still eating, sleeping, and lifting, and you cannot progress every workout, then you're "strong enough" in my mind. This level depends on your gender, age, proportions, genetics, etc.