One Rep Max Calculator - Epley, Brzycki & More

Estimate your 1RM from any set of 1-15 reps using four proven formulas side by side, plus a percentage table for programming your training. Free and browser-based, nothing you enter is stored or sent anywhere.

Units

Estimated one rep max (average of 4 formulas)

114.8 kg

Epley

116.7

Brzycki

112.5

Lombardi

117.5

O'Conner

112.5

This is an indication for training purposes, not medical advice. Never attempt a true max without proper warm-up and a spotter.

Training percentages of your 1RM

% of 1RMWeight (kg)Typical repsTraining focus
95%1092Max strength
90%103.33-4Max strength
85%97.65-6Strength
80%91.87-8Strength / hypertrophy
75%86.19-10Hypertrophy
70%80.311-12Hypertrophy
65%74.613-15Hypertrophy / endurance
60%68.916-20Endurance
55%63.120+Endurance
50%57.420+ / warm-upTechnique / warm-up

How One Rep Max Formulas Work

Your one rep max (1RM) is the heaviest weight you can lift for a single repetition with good form. Testing it directly is taxing and carries injury risk, so coaches estimate it from a submaximal set instead. The four most cited formulas all convert "weight x reps" into a 1RM estimate: Epley (weight × (1 + reps/30)), Brzycki (weight × 36 / (37 - reps)), Lombardi (weight × reps^0.10), and O'Conner (weight × (1 + 0.025 × reps)). For 100 kg lifted 5 times, they give 116.7, 112.5, 117.5, and 112.5 kg respectively, an average of about 115 kg.

The formulas agree closely between 2 and 6 reps and drift apart as reps climb, which is why this calculator caps input at 15 reps. Epley and Brzycki give nearly identical results around 10 reps, while Lombardi tends to run high for low reps and low for high reps. Averaging the four, as this tool does, smooths out individual formula bias. Sets of 3-5 reps taken close to failure give the most reliable estimates; a set of 12+ reps says more about muscular endurance than maximal strength.

The percentage table is where the estimate becomes useful. Classic strength programs prescribe loads as a percentage of 1RM: heavy triples at 90%, fives at 85%, hypertrophy work at 70-75% for 10 reps, and warm-ups around 50%. If your estimated squat 1RM is 140 kg, a "5x5 at 80%" session means 112 kg. Recalculate every 4-6 weeks as you get stronger, and expect your true tested max to sit within roughly 5% of the estimate.

Remember these numbers are training indications, not medical advice. Pair your strength work with the Calorie Calculator or BMR Calculator on ToolForte to match your nutrition to your training volume, and use the BMI Calculator for a quick body composition baseline. All tools are free and run entirely in your browser.

How the One Rep Max Calculator Works

  1. 01Choose kilograms or pounds and enter the weight you lifted.
  2. 02Enter how many reps you completed with that weight (1 to 15).
  3. 03The calculator runs the Epley, Brzycki, Lombardi, and O'Conner formulas side by side and averages them.
  4. 04Use the percentage table to plan training loads from 50% to 95% of your estimated max.

Estimating instead of testing

A true 1RM test is fatiguing and carries injury risk, so most lifters estimate instead. Lift a weight for as many clean reps as possible (3-5 reps close to failure gives the best estimate), then let the formulas extrapolate. For 100 kg x 5 the four formulas give 112.5 to 117.5 kg, averaging about 115 kg. Expect your real tested max to fall within about 5% of that.

When to Use This Tool

Use it when starting a percentage-based program (5/3/1, Starting Strength progressions, powerlifting peaking blocks), when you want to track strength progress without maxing out, or to convert a rep PR into an estimated max. Recalculate every 4-6 weeks as your training weights move up.

Common Use Cases

Tips

  • Use sets of 3-5 reps close to failure for the most accurate estimate.
  • Recalculate every 4-6 weeks; your percentages should follow your progress.
  • Round working weights down to the nearest plate increment rather than up.

Frequently Asked Questions

Which 1RM formula is most accurate?→
For 2-6 reps the formulas agree within a few percent, so it barely matters. Brzycki tends to be slightly conservative at higher reps, Epley slightly generous, and Lombardi runs high at very low reps. Averaging all four, as this calculator does, smooths out the individual biases.
How many reps should I use for the best estimate?→
3 to 5 reps taken close to failure give the most reliable estimate. Sets above 10 reps measure muscular endurance as much as strength, and above 15 reps the formulas become so inaccurate that this calculator does not accept them.
What are the four formulas exactly?→
Epley: weight x (1 + reps/30). Brzycki: weight x 36 / (37 - reps). Lombardi: weight x reps^0.10. O'Conner: weight x (1 + 0.025 x reps). For 100 kg x 5 they give 116.7, 112.5, 117.5, and 112.5 kg respectively.
How do I use the percentage table for training?→
Strength programs prescribe loads as percentages of 1RM. With an estimated max of 140 kg, a set of 5 at 85% means 119 kg, and hypertrophy work at 70% for 10-12 reps means 98 kg. The table shows the typical rep range each percentage supports.
Should beginners test their real 1RM?→
Generally no. Estimated maxes are safer and accurate enough for programming. If you do test a true max, do it fresh, after a thorough warm-up, with a spotter or safety pins, and not more than a few times per year. This tool is a training indication, not medical advice.

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