How Fitness Bloggers Can Use Calculators to Increase Engagement

The one rep max (1RM) is the maximum amount of weight you can lift for a single repetition of any exercise. It is the gold standard for measuring strength and the foundation of effective programming for powerlifters, bodybuilders, and recreational gym-goers alike.

Why 1RM Matters

Knowing your 1RM allows you to programme training percentages precisely. Research shows that different rep ranges at different percentages of 1RM produce different training adaptations. Working at 85–95% of 1RM develops maximum strength. Working at 67–85% develops hypertrophy. Working at 50–67% develops muscular endurance.

How to Calculate 1RM Without Maxing Out

You do not need to perform a true max lift to estimate your 1RM. The Epley formula — one of several validated equations — estimates 1RM from a submaximal set: 1RM = weight × (1 + reps/30). For example, if you bench press 80kg for 8 reps, your estimated 1RM is 80 × (1 + 8/30) = 80 × 1.267 = approximately 101kg.

Other validated formulas:

• Brzycki: weight × (36 / (37 − reps))
• Lander: weight / (1.013 − 0.0267123 × reps)
• O’Conner: weight × (1 + 0.025 × reps)

Using 1RM for Training Percentages

Once you have your 1RM, use it to set training loads. For strength work, target 80–90% of 1RM for 3–5 sets of 3–5 reps. For hypertrophy, target 65–80% for 3–4 sets of 6–12 reps. FitNFO Pro includes a Rep Max Percentage Calculator to do this automatically.