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1RM Calculator

reps

Formulas are most accurate for sets of 2–10 reps taken to (or within 1 rep of) muscular failure. Above 10 reps, estimates can drift by ±15–20%.

Solution

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Brzycki (most cited)

Linear-regression fit by Matt Brzycki (1993). Best behaved for sets in the 2–10 rep range; accuracy degrades sharply above 10 reps because the denominator shrinks toward zero near reps ≈ 37.

1RM = w / (1.0278 − 0.0278 × reps)

Epley

Published by Boyd Epley (1985). Slightly higher estimates than Brzycki in the 3–10 rep range and the most common alternative; widely used by collegiate strength programs.

1RM = w × (1 + reps / 30)

Lombardi

Power-law fit (Lombardi, 1989). Tracks closely with Epley at typical hypertrophy rep ranges and tends to be the most generous of the four above 6 reps.

1RM = w × reps^0.10

O'Conner

Linear estimator by O'Conner et al. (1989). Produces results similar to Brzycki for sets of 5 or fewer; conservative compared to Epley and Lombardi.

1RM = w × (1 + 0.025 × reps)

How It Works

The one-rep max (1RM) is the heaviest weight you can lift one time with proper form on a given exercise. Actually testing a 1RM is fatiguing and risky outside of a controlled meet setting, so coaches use regression formulas to estimate it from a lighter, multi-rep set. This calculator runs your weight × reps through four published equations (Brzycki, Epley, Lombardi, O'Conner) and shows the estimates side-by-side, then converts the primary 1RM into a percentage table you can use to pick working weights for strength, hypertrophy, and endurance days.

Example Problem

A lifter benches 100 kg for 5 clean reps to near-failure and wants to estimate their 1RM so they can program their next training block.

  1. Identify the knowns. Tested weight w = 100 kg, completed reps = 5 (a moderate hypertrophy set, well within the ≤10-rep range where these formulas are accurate).
  2. Apply the Brzycki formula: 1RM = w / (1.0278 − 0.0278 × reps) = 100 / (1.0278 − 0.139) = 100 / 0.8888 ≈ **112.5 kg**.
  3. Apply Epley as a cross-check: 1RM = w × (1 + reps / 30) = 100 × (1 + 5/30) = 100 × 1.1667 ≈ **116.7 kg**.
  4. Apply Lombardi: 1RM = w × reps^0.10 = 100 × 5^0.10 ≈ 100 × 1.1747 ≈ **117.5 kg**.
  5. Apply O'Conner: 1RM = w × (1 + 0.025 × reps) = 100 × (1 + 0.125) = **112.5 kg**.
  6. The four estimates span 112.5–117.5 kg — a ±2.5 kg / ±2% spread, which is the typical disagreement at 5 reps. Take the average (≈115 kg) as the working 1RM and use the percentage table to pick training weights: 80% × 115 = 92 kg for sets of 8, 70% × 115 = 80 kg for sets of 12, and so on.

Key Concepts

All four 1RM formulas are population-mean regressions fit on bench press, squat, and deadlift data. Accuracy is best in the 2–10 rep range (±5%); above 10 reps the estimates can diverge by ±15–20% and Brzycki's denominator approaches zero, blowing up the prediction. The formulas disagree most for big compound lifts at low rep counts (Lombardi and Epley run ~3–5% higher than Brzycki at 5 reps) and least at 1–2 reps where all four collapse toward the tested weight. The percentage-of-1RM table below uses the standard NSCA prescription chart for matching intensity to rep target.

Applications

  • Programming working weights: pick a percentage of your 1RM (e.g., 75% × 1RM for sets of 10 hypertrophy) without actually testing a max.
  • Tracking strength gains: estimate 1RM from heavier multi-rep sets across a training block and graph the trend over months.
  • Powerlifting attempt selection: estimate openers, second, and third attempts from a peaking-block top set.
  • Cardiac rehab and beginner training: avoid the injury risk of true 1RM testing by deriving training intensity from a safer 5–10 rep set.

Common Mistakes

  • Using a set with reps in reserve. The formulas assume the tested set was taken to true muscular failure (or within 1 rep of it). Estimating from an easy set of 5 overstates 1RM by 5–15%.
  • Plugging in high-rep sets (15+). All four formulas were fit on data from low-to-moderate rep ranges; above 10 reps the estimates diverge by ±15–20% and Brzycki in particular becomes unreliable.
  • Comparing 1RMs across exercises. The formulas were derived from bench, squat, and deadlift sets. Accuracy is poorer on isolation lifts (curls, lateral raises) where local muscular endurance dominates over absolute strength.
  • Treating one formula's answer as exact. Even within the valid rep range, the standard deviation of estimate vs. measured 1RM is ±5% per formula — always check at least two and consider the spread.

Frequently Asked Questions

What is a 1RM?

1RM stands for one-rep max — the heaviest weight you can lift one time with proper form on a given exercise. It is the foundation of strength programming: most prescriptions are written as a percentage of 1RM (e.g., 5×5 at 80% 1RM). Because actually testing a 1RM is fatiguing and carries injury risk, coaches usually estimate it from a lighter multi-rep set using formulas like Brzycki and Epley.

How accurate are 1RM formulas?

In the 2–10 rep range, all four formulas (Brzycki, Epley, Lombardi, O'Conner) typically estimate 1RM within ±5% of a measured max for the big compound lifts. Above 10 reps the error widens to ±15–20%, and Brzycki in particular becomes unreliable because its denominator (1.0278 − 0.0278 × reps) shrinks toward zero. For programming purposes the agreement is usually close enough; for absolute strength comparison, an actual 1RM test in a meet setting is the gold standard.

Which 1RM formula should I use?

Brzycki is the most widely cited and works well for 2–10 reps; Epley tends to run 2–4% higher than Brzycki and is preferred by many collegiate strength programs. Lombardi is the most generous of the four above 6 reps. The practical advice is to run at least two formulas and average them, or to use the formula your strength coach or program author specifies so your prescription numbers stay consistent over time.

What weight is 80% of my 1RM?

Multiply your estimated 1RM by 0.80. The table on this page does it for you across 50%–100% in 5% steps and shows the typical rep target for each band. As examples: 80% × 1RM is the conventional intensity for sets of 8 (hypertrophy work), 70% × 1RM is sets of 12 (volume / metabolic stress), and 90% × 1RM is sets of 3–4 (max strength).

Why does the Brzycki formula differ from Epley?

The two equations were fit on different datasets and use different functional shapes. Brzycki (1993) is a linear interpolation that hits the tested weight exactly at 1 rep and increases reps relatively slowly. Epley (1985) is a simpler 'percent boost per rep' model that adds about 3.3% to 1RM for every extra rep performed. They agree closely at 1–2 reps and diverge by 3–5% at 10 reps, with Epley higher.

Is it safe to actually test my 1RM?

Testing a true 1RM is generally safe for trained lifters with good technique, a spotter (for bench and squat), and a properly warmed-up workout, but it carries real injury risk that estimation avoids. Powerlifters routinely test 1RMs in meet conditions; novice lifters and anyone in rehab should stick to estimation from a 3–5 rep set. Estimation is also the standard in the published strength-training literature because it lets coaches program without exposing athletes to maximal loads weekly.

How many reps should I do to estimate 1RM?

3–8 reps to near-failure is the sweet spot. Below 3 reps the formulas barely add anything (the prediction is essentially the tested weight) and you've already exposed yourself to near-maximal load. Above 10 reps the regression accuracy degrades and the test becomes more about muscular endurance than strength. A common protocol is 5 reps with 90% of your previous 5RM, which gives a stable, well-validated input to any of the four formulas.

Worked Examples

Powerlifting Peaking Block

What's an intermediate lifter's bench 1RM if they hit 100 kg × 5?

An intermediate raw lifter benches 100 kg for 5 clean reps to near-failure during a peaking block. They want a working 1RM to plan opener, second, and third attempts for an upcoming meet.

  • Knowns: weight w = 100 kg, reps = 5.
  • Brzycki: 1RM = 100 / (1.0278 − 0.0278 × 5) = 100 / 0.8888 ≈ 112.5 kg.
  • Epley: 1RM = 100 × (1 + 5/30) = 100 × 1.1667 ≈ 116.7 kg.
  • Lombardi: 1RM = 100 × 5^0.10 ≈ 100 × 1.1747 ≈ 117.5 kg.
  • O'Conner: 1RM = 100 × (1 + 0.025 × 5) = 100 × 1.125 = 112.5 kg.
  • Average of the four: (112.5 + 116.7 + 117.5 + 112.5) / 4 ≈ 114.8 kg.

Estimated 1RM ≈ 115 kg (range 112.5–117.5)

A common attempt-selection scheme for a first meet: opener at 90% of estimated 1RM (≈ 103 kg, a strong third attempt in training), second at the estimate itself (115 kg), third at 102.5% (≈ 118 kg). Informational only; not coaching advice.

Hypertrophy Programming

What working weights should a lifter use for 8s if they squat 225 lb × 8?

A lifter back-squats 225 lb for 8 reps with one rep in reserve. They want to know their estimated 1RM and pick a working weight for a 4×8 hypertrophy block.

  • Knowns: w = 225 lb, reps = 8.
  • Brzycki: 1RM = 225 / (1.0278 − 0.0278 × 8) = 225 / 0.8054 ≈ 279.4 lb.
  • Epley: 1RM = 225 × (1 + 8/30) = 225 × 1.2667 ≈ 285.0 lb.
  • Average ≈ 282 lb (take 280 lb as the working 1RM).
  • Hypertrophy target = 75–80% × 1RM for sets of 8–10 → 0.775 × 280 ≈ 217 lb.
  • Round to plate math: 215 lb (45 + 45 + 25 + 5 each side) for 4×8.

1RM ≈ 280 lb; program 215 lb × 4 × 8

Note this lifter had 1 rep in reserve on the tested set, so the true 1RM is slightly higher than the estimate (maybe 285–290 lb). The formulas assume a set taken to true failure; reps-in-reserve sets bias the estimate low by 5–10 lb.

Beginner Linear Progression

What does deadlifting 140 kg × 3 imply for a novice lifter's 1RM?

A novice lifter pulls 140 kg for 3 reps at the end of their linear-progression block. They want to know whether to keep adding 5 kg per session or switch to a more advanced program.

  • Knowns: w = 140 kg, reps = 3.
  • Brzycki: 1RM = 140 / (1.0278 − 0.0278 × 3) = 140 / 0.9444 ≈ 148.2 kg.
  • Epley: 1RM = 140 × (1 + 3/30) = 140 × 1.1 = 154.0 kg.
  • Lombardi: 1RM = 140 × 3^0.10 ≈ 140 × 1.1161 ≈ 156.3 kg.
  • O'Conner: 1RM = 140 × (1 + 0.075) = 140 × 1.075 = 150.5 kg.
  • Range: 148–156 kg. Take 152 kg as the working 1RM.

Estimated 1RM ≈ 152 kg

At ~1.7× bodyweight on the deadlift, a typical novice lifter is approaching the end of true linear progression. Switching to a 4-week intermediate program (e.g., Texas Method, 5/3/1 BBB) with the 1RM here as the training max is the standard next step.

1RM Formulas

Each formula below is a regression fit on bench / squat / deadlift data from the published exercise-science literature. They take a tested weight w lifted for reps repetitions to (or near) muscular failure and return an estimated one-rep max:

1RM = w / (1.0278 − 0.0278 × reps)Brzycki (1993) — most widely cited
1RM = w × (1 + reps / 30)Epley (1985) — common in collegiate strength programs
1RM = w × reps^0.10Lombardi (1989) — power-law fit
1RM = w × (1 + 0.025 × reps)O'Conner et al. (1989) — conservative linear fit

Where:

  • 1RM — estimated one-rep max (same units as the tested weight)
  • w — weight lifted in the tested set (kg or lb)
  • reps — number of repetitions completed to (or within 1 rep of) muscular failure

All four formulas are population-mean regressions with a standard deviation of roughly ±5% in their valid range (2–10 reps). Above 10 reps, the estimates can diverge by ±15–20% and Brzycki's denominator approaches zero. For programming purposes, run at least two formulas and average them, or use the formula your strength coach specifies so your training percentages stay consistent over time. Output here is informational only and is not a substitute for coaching judgment or medical advice; testing or training near a true 1RM carries injury risk.

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