One Rep Max Calculator

About One Rep Max Calculator

The Four 1RM Formulas

Formula	Equation	Origin
Epley (1985)	Weight x (1 + Reps / 30)	Boyd Epley, strength coach at the University of Nebraska
Brzycki (1993)	Weight x 36 / (37 - Reps)	Matt Brzycki, published in the Journal of Health, Physical Education, Recreation
Lombardi	Weight x Reps ^ 0.10	Based on power-law relationship between weight and reps
O'Conner	Weight x (1 + 0.025 x Reps)	Linear model, simpler but effective for lower rep ranges

The calculator shows all four results plus their average. Using multiple formulas gives a more reliable estimate than relying on any single one, especially when rep counts are higher (where formulas tend to diverge more).

Formula Accuracy by Rep Range

Reps Performed	Accuracy	Notes
1-5 reps	Very accurate (within 2-3%)	Close to actual 1RM; all formulas agree closely
6-10 reps	Good (within 5%)	Reliable for most training purposes
11-15 reps	Moderate (within 5-10%)	Formulas start to diverge; muscular endurance becomes a factor
15+ reps	Rough estimate only	Too many variables; better to test with a heavier set of fewer reps

For the most accurate estimate, use a set of 3-6 reps taken to within 1-2 reps of failure.

Training Percentage Chart

Once you know your 1RM, use these percentages to select the right weight for your training goal:

% of 1RM	Rep Range	Training Goal	Example (100 kg 1RM)
95-100%	1-2 reps	Maximal strength / peaking	95-100 kg
90-95%	2-3 reps	Strength (neural adaptation)	90-95 kg
85-90%	3-5 reps	Strength	85-90 kg
80-85%	5-8 reps	Strength-hypertrophy	80-85 kg
70-80%	8-12 reps	Hypertrophy (muscle growth)	70-80 kg
60-70%	12-15 reps	Muscular endurance / hypertrophy	60-70 kg
50-60%	15-20+ reps	Endurance / warm-up	50-60 kg

Strength Standards by Lift

These are approximate 1RM benchmarks for adult males (multiply by ~0.6-0.7 for female equivalents). Standards vary by body weight, age, and training history:

Level	Bench Press	Squat	Deadlift	Overhead Press
Beginner (0-6 months)	0.5x BW	0.75x BW	1x BW	0.35x BW
Novice (6-12 months)	0.75x BW	1.25x BW	1.5x BW	0.5x BW
Intermediate (1-3 years)	1x BW	1.5x BW	2x BW	0.65x BW
Advanced (3-5+ years)	1.25-1.5x BW	2x BW	2.5x BW	0.85x BW
Elite	1.5-2x BW	2.5-3x BW	3x+ BW	1x+ BW

BW = body weight. These are rough guidelines based on strength training community data. Individual variation is large.

Why Estimate Instead of Testing?

Approach	Pros	Cons
True 1RM test	Actual maximal strength data	Injury risk, requires spotter, very fatiguing, needs days of recovery
Submaximal estimate (this tool)	Safe, quick, can be done any training day	Slightly less precise, especially above 10 reps

Tips for Accurate Estimates

Tip	Why
Use a 3-6 rep set	Most accurate range for all formulas
Go to near-failure	Leaving 3+ reps in reserve underestimates your 1RM
Use the same lift you want to programme	1RM is lift-specific; bench press strength does not predict squat strength
Retest every 4-8 weeks	Strength changes with training; update your numbers regularly
Average the four formulas	Reduces the bias of any single formula

Worked Example: Estimating a Bench Press 1RM

A lifter benches 80 kg for 5 clean reps to near failure. Plugging the numbers into each formula:

• Epley: 80 x (1 + 5/30) = 80 x 1.1667 = 93.3 kg
• Brzycki: 80 x 36 / (37 - 5) = 80 x 1.125 = 90.0 kg
• Lombardi: 80 x 5^0.10 = 80 x 1.1746 = 94.0 kg
• O'Conner: 80 x (1 + 0.025 x 5) = 80 x 1.125 = 90.0 kg

The four-formula average is 91.8 kg, so a working 1RM of roughly 92 kg is a sensible number to programme off. Note the spread of only about 4 kg between the lowest and highest estimate - that tight agreement is typical in the 3-6 rep range, which is exactly why coaches test there. If the same lifter had done 80 kg for 12 reps, Epley would predict 112 kg and Brzycki 115.2 kg, but Lombardi would jump to 100.5 kg. Wider spread means less certainty, so the higher-rep test is only useful if you can't safely go heavier.

How Do the Formulas Compare in Research?

Peer-reviewed accuracy studies generally find the Epley and Brzycki formulas track true 1RM within 2-5% when the test set is 10 reps or fewer. LeSuer and colleagues tested five prediction equations against measured 1RMs in the bench press, squat, and deadlift (Journal of Strength and Conditioning Research, 1997) and found Mayhew, Epley, and Brzycki were the most accurate for bench press, while the squat and deadlift were harder to predict (deadlift in particular tends to be under-estimated because posterior-chain lifts show less fatigue per rep than pressing lifts). A 2018 validation study at Southern Illinois University compared Brzycki and Epley against measured 1RMs in trained lifters and reported mean absolute errors of 1.8% to 3.1% in the 3-10 rep range.

In practical terms this means the four-formula average in this calculator is typically accurate to within a 2-3 kg band in the lower rep ranges - tight enough to programme a strength block, not tight enough to use for a powerlifting attempt on meet day. For competition testing, the sport-specific rule is still to work up to an actual heavy single under supervision.

The target heart rate calculator is useful on conditioning days that follow heavy strength sessions, where staying below lactate threshold helps recovery.

What Rep Range Should I Train In?

NSCA load recommendations pair intensity zones with clear training goals: 85%+ for strength, 67-85% for hypertrophy, and under 67% for muscular endurance (NSCA Load and Repetition Assignments table). The table in this tool follows those zones so you can pick a weight that matches the block you are running.

Training Goal	% of 1RM	Reps per Set	Rest Between Sets
Maximal strength	85-100%	1-5	3-5 minutes
Hypertrophy	67-85%	6-12	1-2 minutes
Muscular endurance	<67%	12-20+	30-60 seconds
Power (explosive lifts)	30-60% (Olympic: 80-90%)	3-6	2-5 minutes

Rest intervals are drawn from the NSCA Essentials of Strength Training and Conditioning (4th edition). Strength work uses long rests because the nervous system needs time to recover between maximal efforts. Hypertrophy work uses shorter rests to drive the metabolic stress that contributes to muscle growth.

Common Mistakes That Throw Off Your 1RM Estimate

• Leaving too many reps in the tank. A submaximal set only predicts 1RM accurately if it is close to failure. If you rack the bar with three clean reps still in reserve, the formula will under-call your real 1RM by 10-15%.
• Testing on a fatigued day. If you test at the end of a heavy week, your nervous system is already depleted. Do the test rep on the first or second working set of a fresh session.
• Applying one lift's 1RM to a different lift. Bench press strength does not predict squat strength and deadlift strength does not predict overhead press strength. Estimate 1RM separately for each lift you want to programme.
• Sloppy technique on the test set. A bounced bench rep or a quarter squat inflates the number and makes your programmed percentages too heavy on later sessions.
• Using a stale 1RM for months. Strength drifts up (or down) with training. A 1RM from eight weeks ago is probably no longer accurate - re-test with a heavy triple or five to update.

How This Tool Fits Into Programming

Most evidence-based strength programmes - 5/3/1, Starting Strength, nSuns, Sheiko variants - run weekly loads off a training max that is 85-90% of your true 1RM. Using an estimated max from a heavy triple or five is usually safer than testing a real single, especially for intermediate lifters who can make progress on percentage-based progression without ever attempting a true 1RM. The calculator's average is designed to plug straight into that kind of programme.

For fuelling the work, the protein calculator shows the 1.6-2.2 g/kg daily range that the International Society of Sports Nutrition recommends for resistance-trained adults, and the calories burned calculator estimates the energy cost of a weight training session. All calculations on this page run in your browser with no data stored.

Kilograms or Pounds?

The calculator supports both kg and lbs via the toggle at the top. The underlying formulas are unit-agnostic - weight goes in, weight comes out, so the unit you enter is the unit you receive. If you train in pounds but read programmes written in kilograms, 1 kg is 2.2046 lbs, so a 225 lbs bench max is roughly 102 kg. Most UK and EU lifters use kilograms; most US lifters use pounds. Competition powerlifting federations (USAPL, IPF, USPA) record attempts in kilograms regardless of where the meet is held, so if you are training toward a meet, it is worth getting used to thinking in kg.

One practical note on plate maths: a typical commercial gym offers 45 lbs (20.4 kg) or 20 kg plates. Converting a kilogram-based programme straight across to pounds can leave you with awkward small-plate stacks, and the other way round too. When in doubt, round to the nearest loadable increment rather than chasing decimals.

Sources

• Brzycki, M. (1993) - Strength Testing: Predicting a One-Rep Max from Reps-to-Fatigue, Journal of Physical Education, Recreation & Dance 64(1): 88-90
• NSCA - Training Load Chart (percentage of 1RM by rep max)
• NSCA - Essentials of Strength Training and Conditioning (load, rep, rest recommendations)
• Validation of the Brzycki and Epley Equations - Southern Illinois University (2018)
• LeSuer et al. (1997) - The Accuracy of Prediction Equations for Estimating 1RM, Journal of Strength and Conditioning Research 11(4)
• ISSN Position Stand - Protein and Exercise (Jager et al., 2017)