"How Heavy Should I Go?" Has a Clear Answer
One of the first questions every lifter hits is: "How much weight should I use for this exercise?"
Go too light and your muscles don't get enough stimulus; go too heavy and your form breaks down, inviting injury. Most people pick a weight "by feel" — and then wonder why they've stalled.
The truth is, the right weight can be derived logically from your goal and your 1RM (one-rep max). This article explains what 1RM is, how to calculate it, and how to set the ideal weight for strength, hypertrophy, or endurance.
What Is 1RM?
1RM (One Repetition Maximum) is the heaviest weight you can lift for exactly one rep with good form. It's the benchmark of your strength — the "measuring stick" for your training.
More broadly, RM (Repetition Maximum) means the maximum number of reps you can complete with a given weight before failure. If 80kg is your limit for 5 reps, then 80kg is your 5RM.
Once you know your 1RM, you can design "how much weight should I use for this goal?" as a simple percentage.
You Can Estimate Your 1RM Without a Max Attempt
"So should I just try a true one-rep max?" No — attempting a genuine 1RM as a beginner is risky. A limit-weight lift with shaky form leads straight to injury.
Instead, use a formula that estimates your 1RM from your normal sets. The two most common are:
Epley: 1RM = weight × (1 + reps ÷ 30)
O'Connor: 1RM = weight × (1 + reps ÷ 40)
For example, if you lift 60kg for 10 reps, the Epley formula gives:
60 × (1 + 10 ÷ 30) = about 80kg
So you can estimate your 1RM from your regular training — no dangerous max attempt required.
Formula results are estimates, and the math is tedious by hand. GymGrid's 1RM calculator does it automatically from your exercise, weight, and reps — and shows the average across multiple formulas.
Goal-Based Weight Selection
Once you know your 1RM, all that's left is deciding what percentage of it to use. The optimal intensity (weight) and rep range differ clearly by goal.
- Strength (maximal force) — 85%+ of 1RM / 1–5 reps. Trains the nervous system and raises the weight you can move.
- Hypertrophy (building size) — 70–85% of 1RM / 8–12 reps. The classic zone if your goal is bigger muscles.
- Endurance — ≤60% of 1RM / 15+ reps. Builds muscle that resists fatigue over time.
For example, if your squat 1RM is 100kg and you're chasing hypertrophy, 70–85kg for 8–12 reps is the sweet spot.
How to Use an RM Chart
If calculating your 1RM and percentages every session sounds like a hassle, an RM chart is your friend.
An RM chart maps "the weight you can lift for N reps" to "roughly X% of your 1RM." Common reference points:
- 1 rep to failure → 100% of 1RM
- 5 reps to failure → ~85% of 1RM
- 8 reps to failure → ~80% of 1RM
- 10 reps to failure → ~75% of 1RM
- 15 reps to failure → ~65% of 1RM
The trick is to use it in reverse. Want a weight that brings you to failure at 10 reps for hypertrophy? Pick ~75% of your 1RM — done, at a glance.
The table below is a quick reference for finding your working weight from your 1RM (up to 100kg) and target reps. Find your 1RM row and read across to the rep count you want.
| 1RM | 1 reps 100% | 3 reps 90% | 5 reps 85% | 8 reps 80% | 10 reps 75% | 12 reps 70% | 15 reps 65% |
|---|---|---|---|---|---|---|---|
| 100kg | 100 | 90 | 85 | 80 | 75 | 70 | 65 |
| 90kg | 90 | 81 | 76.5 | 72 | 67.5 | 63 | 58.5 |
| 80kg | 80 | 72 | 68 | 64 | 60 | 56 | 52 |
| 70kg | 70 | 63 | 59.5 | 56 | 52.5 | 49 | 45.5 |
| 60kg | 60 | 54 | 51 | 48 | 45 | 42 | 39 |
| 50kg | 50 | 45 | 42.5 | 40 | 37.5 | 35 | 32.5 |
| 40kg | 40 | 36 | 34 | 32 | 30 | 28 | 26 |
GymGrid's RM chart builds this table around your own logged lifts and instantly shows the weight for your target reps.
Where to Start as a Beginner
"But what if I don't even know my 1RM yet?" The answer is simple.
Start light and lock in your form
Treat your first few sessions as a window to groove correct technique, not to chase weight. Use just the bar or light dumbbells to learn the movement.
Adding weight before your form is solid means the target muscle doesn't get worked — and your injury risk climbs.
Pick a weight you can do ~10 reps with 2–3 in reserve
Once your form is comfortable, choose a weight where you could do about 10 reps but still have 2–3 left in the tank. That's "leaving reps in reserve" (RIR 2–3) — a safe, sustainable intensity for beginners.
From there, estimate your 1RM and you can transition to goal-based percentages.
Add weight gradually (progressive overload)
Once you can hit your target reps comfortably at a given weight, bump it up in small 2.5–5kg increments. This is progressive overload — the fundamental driver of muscle growth.
Increasing weight gradually requires a record of "what weight and how many reps you did last time." For why logging accelerates your progress, see 5 reasons you should track your workouts.
Common Mistakes
Three weight-selection mistakes to avoid:
- Ego lifting — loading more than you can handle, wrecking your form
- Maxing out every session — always going to your limit outpaces recovery, causing injury and plateaus
- Going too light to challenge yourself — leaving too much in reserve under-stimulates. Aim for "just barely" at your target reps
Heavier isn't automatically better. What matters is whether the weight matches your goal.
Summary
- Your 1RM (max for one rep) is the basis for setting weight
- No dangerous max attempt needed — estimate it from normal sets with Epley, etc.
- Strength = 85%+ / Hypertrophy = 70–85% / Endurance = ≤60%
- Reverse-read an RM chart to find "the weight for your target reps"
- Beginners: light weight for form → leave reps in reserve → progressive overload
Calculating your 1RM and goal-based weights by hand every time is a chore. GymGrid auto-estimates your 1RM from your logged weight and reps, helping you set the right weight for your goal. Start choosing your weights with confidence from today's session.
