How to Select the Correct Weight in the Gym (With Calculator)

Mastering Progressive Overload: A Guide to Muscle Growth

If a training plan looks something like this:

Shoulder Press

10kg x 10
10kg x 10
10kg x 10 🥱

...it's a sign that the programme might not be using progressive overload effectively, and will likely yield you very little progress.

Doing the exact same weight and reps every set, every session, is more like maintenance than an intentional plan to get stronger.

What Actually Builds Muscle?

Muscle growth occurs when resistance training creates small amounts of muscle fibre damage that the body repairs (this is called hypertrophy) - making those fibres thicker and stronger over time.

The 3 main drivers of hypertrophy are:

1. Mechanical Tension – Generated when lifting heavy loads or using a full range of motion.

2. Muscle Damage – Microscopic tears from challenging exercises, that signal the body to repair and grow.

3. Metabolic Stress – The “burn” you feel from higher-rep sets, linked to cellular swelling and hormonal responses.

In practise, this usually means working close to failure in a controlled way, often using roughly 3 sets of 8-12 reps per exercise, with a focus on progressive overload.

The Real Problem: Choosing The Right Weight

A common issue is not knowing:

• What weight to start with
• When to increase or decrease the load mid-session
• How to progress from one session to the next

To make this simpler, the Team RH 8-12 Rep Rule has been built into this calculator - but it's worth learning the logic so you're not relying on the tool mid-workout.

The Team RH 8-12 Rep Rule

The Core Idea

Rather than deciding every set in advance on paper, the weight someone uses during their workout should be guided on their performance.

There are two parts:

1. In-Set Rule - What to do for the next set in the same workout
2. Next Workout Rule - Where to start in the next session

1️⃣ The In-Set Rule

After each set, adjust the weight based on how many reps were achieved:

• 8 reps > Drop the weight next set
• 9 reps > Drop the weight next set
• 10 reps > Keep weight the same next set
• 11 reps > Keep weight the same next set
• 12 reps > If it felt easy, increase the weight. If it felt tough, consider staying the same

This constant reassessment means we're always working at the right level of difficulty for that session, rather than just repeating pre-set numbers that might be too easy.

What does this look like in-action? Here's an example...

Set 1: I lift 42.5kg for 10 reps (follow rule above)
Decision: I'm keeping the weight the same

Set 2: I lift 42.5kg for 8 reps (follow rule above)
Decision: I'm dropping the weight to 40kg

Set 3: I lift 40kg for 9 reps

Each set follows the In-Set Rule so effort stays high and progress is targeted.

2️⃣ The Next Workout Rule

For the next session, look at the first set of your last workout and adjust:

• Achieved 8 reps on first set last time > Keep the same weight
• 9 reps > Keep the same weight
• 10 reps > Consider a small increase
• 11 reps > Increase the weight
• 12 reps > Increase the weight

Once the first set is done in the new session, go straight back into using the In-Set Rule for the rest of the workout.

Using the earlier example:

• Last time, Set 1 was 42.5kg x 10 reps
• Next time, they might start at 45kg for Set 1, then let the In-Set Rule guide the rest.

Things to consider

🔢 Percentage Increases

Not all weight jumps are equal, it's dependent on the exercise.

• Leg press: 120kg > 125kg = 4.2% increase
• Shoulder press: 30kg > 32.5kg = 8.3% increase

So the decision to increase at 10 reps might depend on the exercise and how big the jump is. Over time, you should get a feel for what's right.

If a set lands at 7 or 13 reps, treat it similarly to 8 or 12 when deciding whether to go up or down on the next set. It won't always be exact but progress is rarely perfectly tidy.

🆕 If You're New to the Gym

The first session is often about finding starting weights. The rule becomes easier to apply once you've got a rough baseline after a few workouts.

Beginners, or those returning to the gym after a lay-off phase, often see numbers climb quickly at first - this is the 'honeymoon period'. After that, progress slows and becomes a steady grind of small increases, partial extra reps and gradual movements. That slow, consistent work is over months and years is what truly adds up.

⏱ Rest Times

• 3 Minutes rest allows close to full strength recovery
• 1 Minute rest allows for around 50% recovery, which means the next set will feel harder at the same weight.

If time is tight and full 3-minute rests aren't realistic, aim for consistent rest periods each session (for example, 90 or 120 seconds), so it's simpler to compare like-for-like - more like a controlled experiment than guesswork.

🧩 Exercise Order

Try to keep exercise order the same from session to session.

If shoulder press is done before bench press one week, and then after bench press the next, performance will naturally differ. That makes it harder to track genuine strength progress.

Keeping exercise order consistent helps to clearly see whether improvements are coming from increased strength, not just changes in fatigue.

💧Hydration

A well-hydrated body performs 17% better than a dehydrated one. Hydration is one of the simplest ways to support consistent training performance and effective progressive overload.

Water intake is tracked daily in the Team RH App, as many people either overlook it or assume they’re drinking more than they actually are.

🍗 Protein Intake

Getting enough protein helps maintain muscle mass while on a diet and keeps you fuller for longer. You can check out our Protein Calculator