One Rep Max Calculator — Estimate Your 1RM

Weight Lifted

10300

Reps Performed

reps

120

For best accuracy, use a set of 3–8 reps at near-maximal effort. Accuracy decreases above 10 reps.

Estimated 1RM

—kg

Epley + Brzycki average

Training Weights

90%

Strength

1–3 reps

— kg

80%

Hypertrophy

4–8 reps

— kg

70%

Volume

10–15 reps

— kg

What is a One Rep Max?

A one rep max (1RM) calculator estimates the maximum weight you could lift for a single repetition of an exercise, based on a lighter submaximal set you actually performed. Instead of risking injury by attempting a true max lift, you lift a challenging but manageable weight for 3–10 reps and the calculator extrapolates your 1RM using two validated formulas — Epley and Brzycki.

Knowing your 1RM is the foundation of structured strength programming. Training loads are typically prescribed as percentages of 1RM — heavy strength sets at 85–90%, hypertrophy sets at 70–80%, and volume work at 60–70%. Without a 1RM reference, you are guessing your training intensity. With it, you can follow evidence-based progression systems like linear periodization, RPE-based training, or percentage-based programmes used by strength coaches worldwide.

The calculator also outputs your 90%, 80%, and 70% 1RM values as ready-to-load training weights — eliminating the mental arithmetic between sets.

How to use this One Rep Max calculator

Warm up thoroughly before your test set — work up to your test weight in 3–4 graduated warm-up sets.
Perform a near-maximal set — choose a weight you can lift for 3–8 reps but not more. The last rep should be a genuine effort. Avoid sets above 10 reps as accuracy decreases.
Enter Weight Lifted in kg — the load you used for the test set.
Enter Reps Performed — the number of complete, quality reps you completed.
Read your estimated 1RM and note your 90/80/70% training weights.
Load accordingly — use the percentage outputs to set weights for your next training session.

Formula & Methodology

Epley Formula (1985):

1RM = W × (1 + R ÷ 30)

Brzycki Formula (1993):

1RM = W × 36 ÷ (37 − R)

Averaged Estimate:

1RM = (Epley + Brzycki) ÷ 2

Where W = weight lifted (kg), R = reps performed

Training percentage outputs:

90% 1RM = 1RM × 0.90 · 80% 1RM = 1RM × 0.80 · 70% 1RM = 1RM × 0.70

(rounded to nearest 0.5 kg for practical loading)

Worked example:

Bench press set: 90 kg for 5 reps.

- Epley = 90 × (1 + 5 ÷ 30) = 90 × 1.167 = 105 kg
- Brzycki = 90 × 36 ÷ (37 − 5) = 90 × 36 ÷ 32 = 101.3 kg
- Averaged 1RM = (105 + 101.3) ÷ 2 = 103.1 kg ≈ 103 kg
- 90% = 92.5 kg (for heavy doubles/triples)
- 80% = 82.5 kg (for hypertrophy sets of 6–8 reps)
- 70% = 72.5 kg (for volume sets of 10–12 reps)

Assumptions: Formulas assume the test set was performed with consistent technique to technical failure or one rep in reserve. They are most accurate for 1–10 reps; accuracy degrades significantly above 12–15 reps. Results are specific to the tested exercise and movement pattern — a bench 1RM cannot be used to predict squat strength. Track strength alongside body composition using the Lean Body Mass Calculator to monitor strength-per-kg-of-lean-mass over training cycles.

Frequently Asked Questions

What is a one rep max (1RM)?

A one rep max (1RM) is the maximum weight you can lift for exactly one complete repetition with proper form for a given exercise. It is the gold standard measure of absolute strength in resistance training and is used to set training loads as percentages of 1RM (e.g. 80% of 1RM for 8 reps). Testing your actual 1RM involves maximal effort and some injury risk — the one rep max calculator estimates it safely from submaximal lifts.

How accurate is the 1RM calculator?

The calculator averages the Epley and Brzycki formulas, both of which have been validated in peer-reviewed research. For sets of 1–6 reps, the estimate is typically within 2–5% of actual 1RM. Accuracy decreases for sets above 10 reps because factors like local muscular endurance, mental fatigue, and technique become more influential than pure strength. For the best estimate, use a set of 3–5 reps at near-maximal effort.

What is the Epley formula for 1RM?

The Epley formula is: 1RM = Weight × (1 + Reps ÷ 30). It was developed by Boyd Epley in the 1980s and is one of the earliest and most widely used 1RM estimation formulas. It slightly overestimates 1RM at higher rep ranges (above 10 reps) but is highly accurate for sets of 1–8 reps. This calculator averages Epley with the Brzycki formula for a more balanced estimate.

What is the Brzycki formula for 1RM?

The Brzycki formula is: 1RM = Weight × 36 ÷ (37 − Reps). Developed by Matt Brzycki, it tends to be slightly more conservative than Epley and performs particularly well for rep ranges of 2–10. It becomes mathematically undefined at 37 reps (the denominator reaches zero), but this is not a practical limitation as 1RM estimation above 15–20 reps is unreliable regardless of formula.

What percentage of 1RM should I train at?

Training intensity depends on your goal. For maximum strength development (1–5 reps), train at 85–100% of 1RM. For hypertrophy/muscle building (6–12 reps), train at 67–85% of 1RM. For muscular endurance (15+ reps), train at below 67% of 1RM. The calculator shows your 90%, 80%, and 70% 1RM values as ready-to-use loading targets for each rep range.

Can I use the 1RM calculator for all exercises?

The formulas work best for compound barbell movements — squat, deadlift, bench press, overhead press, and barbell row — where technique is consistent across rep ranges. They are less reliable for machine exercises (which assist stabilisation), dumbbell exercises (which require more balance), and isolation exercises (where local muscular endurance limits performance before neural strength does). Use the estimate as a starting point and adjust based on how the actual weight feels.

How should I test for my sub-maximal lift for 1RM calculation?

Warm up thoroughly and work up to a weight you can lift for 3–6 reps with excellent form but near-maximal effort on the last rep. The set should feel like a 9–10 out of 10 on the perceived effort scale. Enter that weight and rep count into the calculator. Avoid using a weight you can lift for 15+ reps — the estimate becomes unreliable. Sets of 3–5 reps typically give the most accurate 1RM predictions.

How often should I retest my 1RM?

For most training goals, recalculate your 1RM every 4–8 weeks using a heavy submaximal set — you do not need to attempt an actual 1RM max test in every training block. As you get stronger, your working weights at a given rep range will increase, automatically updating the 1RM estimate. Actual 1RM testing (peaking blocks) is typically done 2–3 times per year for powerlifters and competitive athletes.

What is the difference between absolute and relative strength?

Absolute strength is your 1RM in kg — how much total weight you can lift. Relative strength is your 1RM divided by your body weight — how strong you are relative to your size. A 70 kg person benching 100 kg (1.43× bodyweight) is relatively stronger than a 100 kg person benching 120 kg (1.2× bodyweight) even though the absolute lift is lower. Use your 1RM alongside your body weight and the [Lean Body Mass Calculator](/lean-body-mass-calculator/) to track strength per kg of lean mass over time.

Is it safe to attempt a true 1RM lift?

Testing a true 1RM carries a higher injury risk than submaximal training, particularly for exercises like the deadlift and squat where a missed lift can cause falls or acute strain. Best practice is to have a spotter, warm up extensively, approach the max weight gradually over multiple sets, and attempt the true 1RM only after establishing a conservative estimate using a submaximal test. Using the calculator to estimate from a 3–5 rep set eliminates this risk entirely for most training purposes.

How does 1RM relate to calorie burn during strength training?

Training at higher percentages of 1RM (heavy strength work) burns fewer calories per session than high-volume hypertrophy training (more reps, shorter rest). However, heavier training builds more dense muscle tissue over time, which increases your resting metabolic rate — creating a long-term calorie burn advantage. For calorie burn during sessions, use the [Calories Burned Calculator](/calories-burned-calculator/) with 'Weight Training' selected.