1RM Calculator

What is a one rep max (1RM)?

A one rep max, commonly written as 1RM, is the maximum amount of weight you can lift for exactly one full repetition of a given exercise with correct technique. It is the most direct measure of absolute strength and the foundation for percentage-based programming in powerlifting, Olympic weightlifting, and evidence-based hypertrophy training. When a coach says "work up to 80% of your 1RM for 4 sets of 5," they are referring to 80% of your maximal single-rep capability on that lift.

Knowing your 1RM matters for two reasons. First, it gives you an objective baseline to track strength progress over weeks and months — numbers do not lie the way perceived effort can. Second, it lets you train with precision. Research consistently shows that training intensity (percentage of 1RM) is one of the primary drivers of specific adaptations: high percentages (90%+) develop maximal force production, moderate percentages (70–85%) maximize hypertrophy and strength simultaneously, and lower percentages (60–70%) build muscular endurance and work capacity.

The three 1RM formulas explained

This calculator uses three of the most widely cited and validated 1RM prediction formulas. Each approaches the weight-reps relationship slightly differently, and their outputs converge closely for sets of 1–6 reps while diverging somewhat at higher rep ranges.

The Epley formula (1985) is the most commonly cited: 1RM = weight × (1 + reps/30). It tends to produce slightly higher estimates than the other formulas, especially at moderate rep ranges of 8–12. The formula was derived empirically and works well for standard barbell exercises.

The Brzycki formula (1993) calculates 1RM = weight × (36 / (37 − reps)). It is considered particularly accurate for low-rep sets (1–10 reps) and tends to be slightly more conservative than Epley at moderate rep ranges. Many strength coaches prefer Brzycki for setting training percentages precisely because of its conservative bias — better to underestimate and progress than to overestimate and miss lifts.

The Lombardi formula (1989) uses an exponential relationship: 1RM = weight × reps^0.10. It tends to produce the most conservative estimates, especially at higher rep counts. Some research suggests it performs well for intermediate lifters performing sets of 4–8 reps.

The average of all three formulas is generally the most defensible estimate for everyday training purposes. It smooths out the biases of each individual formula and gives you a reliable baseline for setting training weights.

How to use the 1RM calculator safely

The safest way to use this calculator is to perform a near-maximal set with good technique rather than attempt a true single-rep maximum. Load a weight you can perform 3–6 reps with, push to within 1–2 reps of failure (not complete failure), and enter your weight and reps into the calculator. This approach minimizes injury risk while still producing an accurate 1RM estimate.

If you do test an actual 1RM — for example, in competition or a structured strength test — follow this protocol: warm up thoroughly with 10–15 minutes of general movement, then perform progressively heavier sets at 60%, 75%, 85%, and 92–95% of your estimated max with full rest between each. Attempt your true max only when you are fully warm and have a spotter or safety equipment in place. Avoid 1RM testing when fatigued, after a deload, or less than 48 hours after a heavy training session.

1RM formulas are most accurate for 1–10 reps. Beyond 15 reps, the relationship between reps and percentage of max becomes highly individual, and prediction error increases significantly. If your set involved more than 15 reps, treat the calculated 1RM as a rough estimate and verify it with a lower-rep test set before building a training program around it.

Using 1RM percentages for progressive overload

Once you know your 1RM, the most evidence-backed approach to building strength is systematic progressive overload — gradually increasing the demands placed on your muscles over time. The training percentage chart in this calculator shows you what weight corresponds to each intensity zone and approximately how many reps you should be able to complete at that intensity.

A simple progressive overload template: start a new training block at 70–75% of your current 1RM for your main compound lifts (bench press, squat, deadlift, overhead press). Each week, add 2.5–5 lbs (or 1–2.5 kg) to the bar while keeping reps constant. When the weight reaches approximately 85% of your starting 1RM, retest your 1RM, recalculate your training weights, and begin the next block. This linear progression model works for beginners and intermediate lifters and typically produces 1RM increases of 5–15% per 8–12 week cycle.

For more advanced lifters, percentage-based programming becomes more sophisticated. Periodization models like Daily Undulating Periodization (DUP) alternate intensity zones across sessions — for example, 80% × 4 on Monday, 70% × 8 on Wednesday, 85% × 3 on Friday — to simultaneously develop multiple strength qualities. The key principle remains the same: track your 1RM regularly, use it to set precise training loads, and ensure those loads progress over time.

For related tools, check out our macro calculator to align your nutrition with your strength goals, or read our guide on progressive overload for a deeper breakdown of how to structure long-term strength progress. If you want to know what a good 1RM looks like for your experience level, see our 1RM standards guide.

Track strength progress over time with Cora

Cora automatically logs your workout data, tracks estimated 1RM trends across sessions, and adjusts your training targets as you get stronger. Instead of manually recalculating percentages every few weeks, Cora handles the programming so you can focus on the training. Download free.