Calculate My 1 Rep Max: Formula & Chart

This calculator estimates your one-repetition maximum (1RM) — the heaviest weight you can lift for a single rep — based on a submaximal set you’ve already completed. You enter the weight you lifted, the number of reps you performed, and the calculator returns your estimated 1RM, plus your estimated strength at several common rep ranges. It uses the Epley formula, which is one of the most widely accepted and validated prediction equations in strength training.

Formula

The Epley formula estimates your one-rep max as:

1RM = W × (1 + R / 30)

Where:

• W = the weight you lifted (in kg or lb — the formula works with any consistent unit)
• R = the number of repetitions you completed with that weight
• 1RM = your estimated one-repetition maximum (in the same unit as W)

The logic behind the formula: each additional rep you can perform with a given weight adds approximately 3.33% to your estimated max. So if you lift 100 kg for 5 reps, your estimated 1RM is 100 × (1 + 5/30) = 116.7 kg. The formula is most accurate for rep ranges between 2 and 10, and becomes less reliable above 10 reps.

Worked Example

Using the default values from the calculator above — a 100 kg lift for 5 reps:

1. Start with the Epley formula: 1RM = W × (1 + R / 30)
2. Plug in the numbers: 1RM = 100 × (1 + 5 / 30)
3. Calculate the fraction: 5 / 30 = 0.1667
4. Add 1: 1 + 0.1667 = 1.1667
5. Multiply by the weight: 100 × 1.1667 = 116.7 kg

So your estimated 1RM is 116.7 kg. The calculator also shows 90% (105.0 kg), 80% (93.3 kg), and 70% (81.7 kg) of that max — useful for planning training loads.

Why Use a 1RM Calculator?

Testing your true 1RM by actually lifting a maximal weight is risky — it places high stress on muscles, joints, and connective tissue, and requires a spotter and careful warm-up. A prediction formula lets you estimate your max from a safer, submaximal set. This is especially useful for:

• Beginners who haven’t yet learned proper technique on heavy lifts
• Lifters who train alone without a spotter
• People with prior injuries who want to avoid maximal loads
• Programs that prescribe percentages of 1RM (e.g., 5×5 at 80%)

Knowing your estimated 1RM helps you set realistic training weights, track progress over time, and compare your strength across different lifts (like bench press vs. squat) on a common scale.

How to Perform the Test Set

For the most accurate estimate, follow this protocol:

1. Warm up thoroughly with light weights and gradually increase the load.
2. Choose a weight you can lift for 2–10 reps with good form, leaving 1–2 reps “in the tank� (i.e., not to absolute failure).
3. Perform the set, counting only clean, full-range reps.
4. Enter the weight and reps into the calculator.

Do not use a weight so light that you can do 15+ reps — the formula overestimates at high rep ranges. Similarly, using a weight you can only lift once or twice gives a less stable estimate because fatigue and technique play a larger role.

Common Mistakes and Limitations

The Epley formula is a statistical estimate, not a measurement. Individual variation means your actual 1RM could be 5–10% higher or lower. Common mistakes include:

• Using reps that aren’t clean — half reps or assisted reps inflate the count and skew the result.
• Mixing units — if you lift in pounds, the result is in pounds; don’t mix kg and lb in the same calculation.
• Testing on an exhausted muscle — the formula assumes a fresh, well-rested lifter. If you test after a hard workout, the estimate will be low.
• Applying it to very high reps — above 10 reps, the linear relationship breaks down; the formula tends to overestimate.

Also note that the formula works best for major compound lifts (squat, deadlift, bench press, overhead press). For isolation movements or exercises with a strong skill component, the estimate is less reliable.

Alternative Formulas

Several other prediction equations exist; they differ slightly in the rep coefficient:

• Epley: 1RM = W × (1 + R/30) — used on this page
• Brzycki: 1RM = W × 36 / (37 − R) — often preferred for higher reps (up to ~12)
• Lombardi: 1RM = W × R^0.10 — a power-based formula
• O’Conner et al.: 1RM = W × (1 + R/40) — more conservative for high reps

For most lifters, the differences between these formulas are small (within a few kg). The Epley formula is a good default because it’s simple and widely used in strength-training literature.

How to Use Your 1RM in Training

Once you have your estimated 1RM, you can use it to set training loads. For example:

• Strength (low reps): 85–95% of 1RM for 1–5 reps
• Hypertrophy (moderate reps): 70–80% of 1RM for 6–12 reps
• Endurance (high reps): 50–70% of 1RM for 15+ reps

Re-test every 4–8 weeks to adjust your percentages as you get stronger. Remember that the estimate is a guide — listen to your body and adjust based on how the weight feels on any given day.

Frequently Asked Questions

How accurate is the 1RM calculator?

For most lifters, the Epley formula predicts the true 1RM within about ±5% when the test set is 2–10 reps. Accuracy depends on technique, fatigue, and individual muscle fiber composition. It’s a useful estimate, not a guarantee.

Can I use the calculator for any exercise?

It works best for large, multi-joint lifts like squat, deadlift, bench press, and overhead press. For smaller or machine exercises, the estimate is less reliable because technique and leverage play a bigger role. Still, you can use it as a rough guide for any lift.

What if I can only do 1 rep?

If you can only do 1 rep, the formula gives W × (1 + 1/30) = W × 1.033, which is very close to the actual weight. In that case, you might as well just record the weight as your 1RM. The formula is more useful when you’re working in the 3–8 rep range.

Should I test to failure?

No. The formula is designed to work with a submaximal set where you stop 1–2 reps short of failure. Testing to failure increases injury risk and fatigue without improving accuracy. Stop when you feel you have 1–2 reps left.

Does the formula work for women and older lifters?

Yes, the Epley formula is based on general strength relationships and applies regardless of sex or age, provided the test set is performed with proper form and a realistic rep range. Individual variation is larger than any group difference.

How often should I recalculate my 1RM?

Every 4–8 weeks is typical, or whenever you feel your strength has changed significantly. Re-test using the same exercise and protocol to track progress accurately. Don’t re-test daily — it’s not necessary and can lead to overtraining.

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in w | Weight lifted | kg | 100 | 0
in r | Reps performed | reps | 5 | 1
out orm | Estimated 1RM | kg | w * (1 + r / 30) | 1
out pct90 | 90% of 1RM | kg | orm * 0.9 | 1
out pct80 | 80% of 1RM | kg | orm * 0.8 | 1
out pct70 | 70% of 1RM | kg | orm * 0.7 | 1