1 Rep Max Calculator

What Is a One-Rep Max?

Your one-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It's the gold standard for measuring absolute strength and serves several practical purposes:

• Programming training percentages — Most strength programs prescribe loads as a percentage of your 1RM (e.g., "5×5 at 80%").
• Tracking progress — A rising estimated 1RM confirms your training is working, even if you never test a true max.
• Comparing strength levels — 1RM relative to bodyweight lets you benchmark yourself against standardized strength tables.

Directly testing your 1RM carries injury risk and requires peak readiness. Submaximal estimation — lifting a lighter weight for multiple reps and calculating from there — is safer, more practical, and something you can do any training session.

How 1RM Formulas Work

All 1RM formulas model a mathematical relationship between the weight lifted and the number of reps performed. They assume that as reps increase, the weight you can handle decreases in a predictable curve. Each formula fits that curve slightly differently:

No single formula is universally best — accuracy varies by exercise, rep range, and individual training level. This calculator averages all six to produce the most reliable estimate possible.

Worked Example: 100 kg for 5 Reps

Take a bench press: 100 kg, five clean reps, the fifth one slow. Here are the three formulas most often quoted, with every term filled in.

Five kilograms separate the highest from the lowest, on a bar loaded to 100 kg. That's one small plate per side. Averaged with the three others this calculator runs, the answer comes out at 115 kg, and any of the six would have been a defensible number to programme from.

Epley multiplies by a straight line, so each rep adds a fixed 3.33% of the working weight. Brzycki divides by a shrinking denominator, which means its curve steepens as reps climb. Lombardi raises reps to a fractional power, so its curve flattens instead. At five reps the three barely disagree. Push the rep count up and they come apart.

Where the Formulas Come Apart

Same 100 kg bar, different rep counts, three formulas. Watch the last column.

Computed from the published equations. Epley = w(1 + r/30); Brzycki = 36w/(37 − r); Lombardi = w·r^0.10.

Below ten reps the spread stays under 8 kg, which on a heavy bench is a rounding decision. At twelve it doubles. At twenty, Brzycki claims 211.8 kg and Lombardi claims 134.9 kg for the same set, a 77 kg argument about one lifter.

There's a quirk worth knowing at ten reps: Epley and Brzycki return the identical 133.3 kg. It isn't luck. Set 1 + r/30 equal to 36/(37 − r) and ten is the crossing point, which is why the two most-cited formulas agree exactly there and diverge in opposite directions either side of it. Under ten reps Brzycki reads lower; over ten it runs away upward.

Turning a 1RM Into a Training Programme

An estimate is only useful if it sets loads. Run the relationship backwards — reps to percentage — and you get the table under every percentage-based programme. The two columns below come from inverting Epley and Brzycki, which is why they meet at ten reps and drift apart above it.

On the 115 kg estimate above, 85% is 98 kg and 75% is 86.5 kg. Those are the two loads that carry most strength programmes: heavy fives around 98 kg to build the top end, sets of ten around 86.5 kg to build the tissue that supports it. The NSCA's guidance in Essentials of Strength Training and Conditioning puts strength work at 85% or above for sets of six or fewer, and hypertrophy work at 67–85% for six to twelve.

One caveat the table hides. The percentages assume you take the set close to failure, and most lifters stop two or three reps earlier than they believe. If your "ten reps at 75%" actually leaves four in the tank, the real percentage was nearer 65% and the estimate above it inflates to match.

When the Estimate Beats a Real Attempt

A true max is a better number. It's also a worse test on most days, and the cost lands on the days around it.

• You're not peaked. A max attempt measures readiness as much as strength. Poor sleep, a hard week, or a heavy session two days ago can drop the bar by 5–10% without your strength having changed at all. A submaximal set for three to five reps carries the same fatigue penalty proportionally, so the estimate stays honest even on a mediocre day.
• Technique breaks before the muscle does. At 100% technique gives way first: the bar path shifts, or a knee caves in. Those are the reps that hurt people. At 85% the same lifter usually just misses the rep.
• You lift alone. A missed bench single without a spotter or safety pins is not a training accident, it's a serious one. Estimation removes the need entirely.
• You want the number often. Testing a real max belongs every 8–12 weeks. An estimate can come off any hard top set, which means you can watch strength trend week to week instead of guessing between tests.
• You're a beginner. Under about a year of training, coordination improves fast enough that a max from six weeks ago is stale, and technique under a true max is rarely reliable yet.

The trade is precision for frequency. LeSuer and colleagues (Journal of Strength and Conditioning Research, 1997) compared seven prediction equations against measured maxes in the bench press, squat and deadlift and found none of them universally best, with accuracy varying by lift. Averaging several, as this calculator does, keeps the error smaller than any single formula's worst case.

How to Test a True Max Without Getting Hurt

If you do want the real number — a meet is coming, or a programme demands it — the NSCA's testing protocol exists precisely so that nobody has to improvise it under a loaded bar.

• 1. Light warm-up. Five to ten reps at a weight that feels easy. Rest one minute.
• 2. Add 10–20% and do three to five reps. Rest two minutes. The bar should still move fast.
• 3. Add another 10–20% and do two to three reps. Rest two to four minutes. This is the last set with any volume in it.
• 4. Add 10–20% again and attempt a single. Rest two to four minutes between every attempt from here.
• 5. Keep adding, in shrinking jumps. Aim to find the max inside five singles. Past that, accumulated fatigue is reading lower than your actual strength.

Non-negotiables around it: a spotter for bench and squat, or safety pins set at the depth you'd need them; a bar you've lifted at 90% before; and a full stop the moment form degrades. Deadlifts don't need a spotter and shouldn't have one — you drop the bar. Do not test a max on a lift whose technique you're still building.

What a Diet Does to the Bar

Strength doesn't survive a deficit for free. Cut calories hard and the estimate on this page will fall, even with training unchanged — partly from glycogen and body water, partly from the nervous system working with less fuel, and partly from lean tissue actually leaving.

Two levers keep most of it. Protein at 1.6–2.2 g per kg of body weight is the range Morton and colleagues (British Journal of Sports Medicine, 2018) arrived at after pooling 49 resistance-training trials, with gains levelling off around 1.6 g/kg in people eating enough overall; a deficit pushes you toward the top of that band. Longland and colleagues (American Journal of Clinical Nutrition, 2016) put young men through four weeks of steep restriction plus hard training, and the group eating 2.4 g/kg gained lean mass while the 1.2 g/kg group lost it.

The second lever is pace. Garthe and colleagues (International Journal of Sport Nutrition and Exercise Metabolism, 2011) had elite athletes lose weight at either 0.7% or 1.4% of body weight per week. Both reached similar leanness, but the slower group came out with more lean mass and better strength numbers. Halving the deficit and doubling the timeline is what protects the total.

Work out your own target with the protein calculator, and read the body recomposition guide if you want to add strength and lose fat at once. Anyone dieting on GLP-1 medication has a harder version of this problem, since suppressed appetite makes protein targets difficult exactly when they matter most — muscle loss on GLP-1 medication covers what the trial data shows.

Strength Standards

These approximate standards express 1RM as a multiple of bodyweight (BW). They provide a rough benchmark for where you stand — not an absolute target.

These numbers are rough guidelines that vary by sex, age, and bodyweight class. They're most useful as directional benchmarks — not strict pass/fail thresholds.

Tips for Increasing Your 1RM

• Progressive overload. Add weight or reps systematically each session or week — not randomly. Even 1 kg per week on bench press adds up to 50 kg in a year.
• Train specifically. To get better at heavy singles, train in the 80–95% range regularly. Strength is a skill that requires practice at high intensities.
• Technique first. A 5% improvement in bar path, bracing, or leg drive can translate to a 10%+ strength increase with zero additional muscle.
• Rest between heavy sets. Take 3–5 minutes between sets of 1–5 reps. Full ATP recovery is critical for maximal force production.
• Eat enough protein. 1.6–2.2 g per kg bodyweight is the evidence-based range for strength athletes. Spread intake across 3–4 meals.
• Sleep 7–9 hours. Growth hormone peaks during deep sleep, and sleep deprivation directly reduces strength output by 5–10%.
• Deload every 4–6 weeks. Reduce volume and intensity by 40–60% for one week. Fatigue masks fitness — you'll often hit PRs the week after a deload.
• Don't test 1RM too often. Every 8–12 weeks is sufficient. Frequent maxing accumulates fatigue without building strength.

1RM Questions Lifters Actually Ask

• How accurate is a 1RM calculator?
  Accurate enough to programme from when the set is 3 to 8 reps taken near failure. In that window Epley, Brzycki and Lombardi land within about 6 kg of each other on a 100 kg bar. At 15 reps that spread grows to 32.6 kg, and at 20 reps to 76.9 kg, which is no longer an estimate of anything.
• Which formula should I use?
  Whichever, if your set was under 10 reps, because they barely disagree there. Above 10 reps Brzycki climbs fastest and Lombardi stays lowest, so the choice starts to matter. LeSuer and colleagues (1997) found no formula best across the bench press, squat and deadlift, which is why this calculator averages six.
• Why do Epley and Brzycki give the same number at 10 reps?
  Because the two curves cross there. Epley adds 3.33% of the working weight per rep in a straight line, Brzycki divides by a shrinking denominator, and the two expressions are equal at exactly 10. Under 10 reps Brzycki reads lower; over 10 it runs higher.
• How many reps should I use for the estimate?
  Three to eight, with one or two reps left in reserve at most. Fewer than three and you are close enough to a real max to inherit its risk. More than eight and the formulas start arguing, because a high-rep set measures conditioning as much as strength.
• Should I test my true one-rep max?
  Only if a competition or a programme requires it, you have a spotter or safety pins, and the lift's technique is solid. Follow the NSCA sequence of warm-up, then singles rising by 10 to 20% with 2 to 4 minutes rest, and find the max inside five attempts. Every attempt past that is fatigue reading as weakness.
• What percentage should I train at?
  85% and above for sets of six or fewer if the goal is strength, 67 to 85% for six to twelve if the goal is size. On a 115 kg estimate that is 98 kg for heavy fives and 86.5 kg for sets of ten.
• Why did my 1RM drop while I was dieting?
  Part of it comes from glycogen and body water, part from a nervous system running on less fuel, and part from lean tissue actually leaving. Protein at 1.6 to 2.2 g per kg and a slower rate of loss protect most of it. Garthe and colleagues (2011) found athletes losing 0.7% of body weight per week held more lean mass and strength than those losing 1.4%.
• Does this work for every exercise?
  Best on the barbell lifts the researchers validated: bench press, squat, deadlift and overhead press. On machines, isolation work and anything where a small muscle fails first, rep performance depends on local endurance rather than maximal force, so the estimate drifts high.