What is a one rep max (1RM)?

A one rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is the gold standard measure of maximal strength in resistance training. The one rep max calculator estimates this value from submaximal lifts so you do not need to actually attempt a risky true 1RM.

How accurate is the one rep max calculator?

The one rep max calculator is most accurate with loads of 3-5 reps — typically within 5% of your true 1RM. Accuracy decreases with higher rep ranges (above 10). For best results, test with a weight you can lift for exactly 3-5 clean reps.

Which 1RM formula is the most accurate?

The Epley and Brzycki formulas are the most widely validated and generally agree within 1-2%. Epley tends to be slightly more accurate for higher rep ranges (6-10), while Brzycki is considered more precise for lower reps (1-5). The one rep max calculator shows all four formulas so you can compare.

How do I use my 1RM for training?

Most strength programs prescribe loads as percentages of your 1RM. For maximal strength, work at 85-95% of 1RM for 1-3 reps. For hypertrophy (muscle growth), use 70-85% for 6-12 reps. For muscular endurance, use 60-70% for 15+ reps. The one rep max calculator generates a full percentage table for your programming.

How often should I recalculate my one rep max?

Recalculate your one rep max every 4-6 weeks or at the start of each training cycle. As you get stronger, your training loads need to increase. Retesting with a heavy 3-5 rep set and using the one rep max calculator keeps your percentages current.

Is this one rep max calculator free?

Yes — this one rep max calculator is completely free to use online. No registration, no payment. Calculate your 1RM and training percentages for any lift, as many times as you need.

Free One Rep Max Calculator Online

This free one rep max calculator estimates your 1RM from submaximal lifts using four proven formulas — use it online to find your maximum strength and generate percentage-based training loads instantly.

Weight Lifted

Reps Performed

Formula

Estimated One Rep Max

—kg

Enter your lift details above

How the One Rep Max Calculator Works

This free online one rep max calculator takes the weight you lifted and the number of reps you completed, then applies a mathematical formula to estimate the heaviest weight you could lift for a single rep. If you bench pressed 100 kg for 5 reps, the Epley formula estimates your one rep max at approximately 116.7 kg.

The one rep max calculator offers four formulas — Epley, Brzycki, Lander, and Lombardi — each derived from different research. The Epley formula uses weight x (1 + reps/30), while Brzycki uses weight x 36/(37 - reps). Both are accurate within about 5% for sets of 3-5 reps.

Once your 1RM is calculated, the tool generates a percentage table from 100% down to 65%. This table is the foundation of percentage-based strength programming used by powerlifters, athletes, and coaches worldwide.

Training with Your 1RM Percentages

90-100% of 1RM (1-3 reps): Pure maximal strength. Used in peaking phases before competitions. Only attempt with a spotter and proper warm-up.

80-90% of 1RM (3-6 reps): The sweet spot for strength gains. Most intermediate programs spend the majority of training time here. A one rep max calculator helps you nail the exact weight for each set.

65-80% of 1RM (6-15 reps): Hypertrophy range. Optimal for muscle growth when combined with adequate volume (12-20 sets per muscle group per week). Use the percentage table to load your working sets precisely.

Tips for Accurate 1RM Estimation

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Test with 3-5 reps for best accuracy. The one rep max calculator becomes less reliable above 10 reps — the math diverges from reality.

›

Use strict form on your test set. Bounced, partial, or assisted reps inflate the weight input and produce an artificially high 1RM estimate.

›

Warm up thoroughly before your test set: 5 reps at 50%, 3 at 70%, 1 at 85%, then your heavy set. Cold muscles underperform.

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Recalculate every 4-6 weeks. Strength changes faster than you think — outdated percentages mean suboptimal training loads.

Frequently Asked Questions

Disclaimer: This free online one rep max calculator provides mathematical estimates for informational purposes only. Actual maximal strength varies based on fatigue, nutrition, sleep, and technique. Never attempt a true one-rep maximum without proper warm-up, a spotter, and appropriate safety equipment. Consult a qualified coach or healthcare provider before beginning a new strength program. This free tool does not replace professional training guidance.

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How the One Rep Max Calculator Works

Training with Your 1RM Percentages

90-100% of 1RM (1-3 reps): Pure maximal strength. Used in peaking phases before competitions. Only attempt with a spotter and proper warm-up.

Tips for Accurate 1RM Estimation

›

Test with 3-5 reps for best accuracy. The one rep max calculator becomes less reliable above 10 reps — the math diverges from reality.

›

Use strict form on your test set. Bounced, partial, or assisted reps inflate the weight input and produce an artificially high 1RM estimate.

›

Warm up thoroughly before your test set: 5 reps at 50%, 3 at 70%, 1 at 85%, then your heavy set. Cold muscles underperform.

›

Recalculate every 4-6 weeks. Strength changes faster than you think — outdated percentages mean suboptimal training loads.