The short answer
Full-body workout: 4 to 6 exercises. Upper-body or lower-body day: 5 to 8 exercises. Push, pull, or legs day: 4 to 6 exercises. A focused 30 minute session: 3 to 4 exercises. Those ranges cover almost every productive workout ever programmed.
But two workouts can both have 6 exercises and deliver totally different results. One uses 2 sets per exercise (12 sets total) and the other uses 4 sets per exercise (24 sets total). The second is twice the training. So treat exercise count as a scheduling question, how many movements fit in your time, and track sets as the training question.
The rule that actually matters: sets per muscle
Aim for 6 to 10 hard sets per muscle group in a single session. A hard set means a set taken close to failure, roughly 1 to 3 reps short of the point where your form breaks. Warm-up sets do not count. Across the week, 10 to 20 sets per muscle is the productive range for most lifters, which is why training each muscle twice per week works so well: 8 sets per session times 2 sessions is 16 weekly sets.
Big muscles need the top of the range, small muscles the bottom. Chest, back, and quads thrive on 8 to 10 sets per session. Biceps, triceps, side delts, and calves usually need only 4 to 6, partly because they already assist on the big compound lifts. Your biceps get real work during every row and pulldown before you ever curl.
Session math: three worked examples
Beginner full-body day, 60 minutes. Six exercises, 3 sets each: squat, bench press, row, Romanian deadlift, overhead press, and a plank or carry. That is 18 total sets. At roughly 3 minutes per set including rest, the lifting takes about 54 minutes, plus a 5 to 10 minute warm-up. Every major muscle gets 3 to 6 sets, perfect for a beginner training 3 days a week.
Intermediate upper day, 70 minutes. Six exercises: bench 3 sets, row 3 sets, overhead press 3 sets, pulldown 3 sets, curl 2 sets, triceps 2 sets. That is 16 sets total, about 48 minutes of lifting at 3 minutes per set, leaving room for warm-up and a little buffer. Chest lands around 6 to 8 hard sets, back around 9 to 12 counting overlap, arms 4 to 6 each.
Short on time, 30 minutes. Pick 3 to 4 compound exercises and do 3 sets each: for example goblet squat, push-up, dumbbell row, and glute bridge. That is 9 to 12 sets in about 27 to 36 minutes. Done 3 times a week, a 30 minute session like this beats a 90 minute session you only do once.
Signs you are doing too many
Sessions longer than 90 minutes are the clearest signal. Past that point, fatigue climbs faster than useful work, and most people start rushing rests or skipping the last exercises. Other signs: your performance drops exercise to exercise instead of holding steady, you are sore for 4 or more days after every session, or you dread training. The fix is subtraction. Cut the least important exercise, the fourth chest movement or the third biceps curl, and watch the important lifts go up.
Junk volume is the related trap: extra sets done with light weights, far from failure, that add fatigue without stimulus. Three hard sets beat six easy ones every time. If you can chat comfortably between every set, the weight is too light to count toward your 6 to 10.
Signs you are doing too few
Sessions under 20 minutes with only 2 or 3 exercises usually undertrain something. Beginners sometimes do bench and curls and call it an upper day, leaving back, shoulders, and triceps untouched. The weekly check catches this: if any major muscle is getting fewer than 10 sets per week across all your sessions, add an exercise for it somewhere. Balance matters more than total count. Six well-chosen exercises covering everything beat ten exercises all for chest.
Put it together for your schedule
Start from your days, not your exercises. Three days a week: full-body days of 5 to 6 exercises each. Four days: upper and lower days of 6 to 7 exercises each. Five or six days: push, pull, and legs days of 4 to 6 exercises each. Then check the weekly set totals per muscle against the 10 to 20 range and adjust. That two-step check, enough sessions to cover everything, enough sets per muscle per week, is the entire planning method in miniature.