How to Calculate Your One-Rep Max From a Set of Reps
This article is general fitness information, not medical advice. If you have an injury, a heart condition or are new to lifting, speak to a GP or qualified coach before heavy training.
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Most training programmes are written as percentages of it, such as “3 sets of 5 at 80%”. The problem is that testing a true 1RM is tiring, needs a spotter and carries more injury risk than a normal session. The good news: you can estimate it closely from a set you already do, such as 100 kg for 5 reps. This guide shows the formulas, how to use them by hand, and how to turn the answer into working weights in kg and lb.
Why estimate instead of testing a true 1RM?
A genuine max attempt is a skill in itself. It needs a proper warm-up ramp, a rested body, safety bars or spotters, and it leaves you fatigued for days. For most people who lift two or three times a week, that is a poor trade. A rep-based estimate gets you within a few percent of the true figure using a set of 3 to 10 reps that you would have done anyway.
Estimating also lets you track progress every week. If your estimated max on the squat rises from 110 kg to 115 kg over a training block, you have got stronger, even though you never attempted a single heavy rep. Both the NHS and the CDC recommend muscle-strengthening activity on at least two days a week for adults, so regular, sustainable sessions matter more than one-off max tests.
The three most-used 1RM formulas
Several researchers have fitted equations to the relationship between weight and reps. Three are used by almost every calculator and app. In each one, w is the weight lifted and r is the number of clean reps completed.
- Epley: 1RM = w × (1 + r ÷ 30)
- Brzycki: 1RM = w × 36 ÷ (37 − r)
- Lombardi: 1RM = w × r0.10
Epley and Brzycki give identical answers at exactly 10 reps. Below 10 reps Epley reads slightly higher; above 10 reps Brzycki climbs faster. Lombardi needs a calculator because of the power, and it tends to sit close to Epley at low reps but lower at higher reps. No formula is “correct” for everyone: people with more fast-twitch muscle often manage fewer reps at a given percentage, while endurance-trained lifters can grind out more. That is why it helps to compare two formulas and use the average.
One quirk worth knowing: plug in a single rep and Epley returns 103.3% of the weight lifted, which is obviously wrong. Good calculators simply return the lift itself when r = 1.
How to calculate your one-rep max step by step
- Choose a recent hard set. Use a set where you stopped close to failure with good technique. Sets of 3 to 10 reps give the most reliable estimates; beyond about 12 reps the error grows quickly.
- Write down the weight and clean reps. Count only reps that met your normal depth and range of motion. Include the bar: an Olympic bar weighs 20 kg (about 44 lb), and many US gyms use a 45 lb bar.
- Apply Epley. Divide reps by 30, add 1, multiply by the weight.
- Apply Brzycki. Subtract reps from 37, divide 36 by that number, multiply by the weight.
- Average and round down. Take the mean of the two and round down to a weight you can actually load. Rounding down is safer than rounding up.
Worked example 1: squat, 100 kg for 5 reps
Sam squats 100 kg (220 lb) for 5 good reps and wants to know his estimated max.
Epley
5 ÷ 30 = 0.1667
1 + 0.1667 = 1.1667
100 × 1.1667 = 116.7 kg
Brzycki
37 − 5 = 32
36 ÷ 32 = 1.125
100 × 1.125 = 112.5 kg
Lombardi (for comparison)
50.10 = 1.1746
100 × 1.1746 = 117.5 kg
Average of Epley and Brzycki
(116.7 + 112.5) ÷ 2 = 114.6 kg
Rounded to a loadable weight: about 115 kg, or roughly 253 lb (115 × 2.20462).
Now Sam can set his working weights. His programme asks for 3 × 5 at 80%:
115 × 0.80 = 92 kg
With 1.25 kg plates the nearest loadable weight is 92.5 kg (20 kg bar plus 36.25 kg each side). If his gym only has 2.5 kg plates, he would use 90 kg or 95 kg, and 90 kg is the sensible choice for a first week.
Worked example 2: bench press in pounds, 185 lb for 8 reps
Jess benches 185 lb (about 84 kg) for 8 reps in a US gym.
Epley: 8 ÷ 30 = 0.2667, so 185 × 1.2667 = 234.3 lb
Brzycki: 37 − 8 = 29, 36 ÷ 29 = 1.2414, so 185 × 1.2414 = 229.7 lb
Average: (234.3 + 229.7) ÷ 2 = 232 lb, rounded down to 230 lb, roughly 104 kg (230 ÷ 2.20462).
At 80% that gives 230 × 0.80 = 184 lb, so she would load 185 lb: a 45 lb bar plus 70 lb each side (a 45 and a 25). Notice that 185 lb is the weight she already lifts for 8, which tells her 80% sets of 5 should feel comfortably hard rather than all-out. That is exactly how a well-chosen percentage should feel.
Reps-to-percentage chart
The same formulas run in reverse tell you what percentage of your 1RM you can typically lift for a given number of reps. Use it to sanity-check a programme or to pick a weight for a target rep range.
| Reps to failure | % of 1RM (Epley) | % of 1RM (Brzycki) | Example if 1RM = 100 kg (220 lb) |
|---|---|---|---|
| 1 | 100% | 100% | 100 kg / 220 lb |
| 2 | 93.8% | 97.2% | 94-97 kg / 207-214 lb |
| 3 | 90.9% | 94.4% | 91-94 kg / 200-208 lb |
| 4 | 88.2% | 91.7% | 88-92 kg / 194-202 lb |
| 5 | 85.7% | 88.9% | 86-89 kg / 189-196 lb |
| 6 | 83.3% | 86.1% | 83-86 kg / 184-190 lb |
| 8 | 78.9% | 80.6% | 79-81 kg / 174-178 lb |
| 10 | 75.0% | 75.0% | 75 kg / 165 lb |
| 12 | 71.4% | 69.4% | 69-71 kg / 153-157 lb |
(The Epley 1-rep figure is shown as 100% because, as noted above, the raw formula over-reads at a single rep.)
Tips for a more accurate estimate
- Use a fresh set. Your first work set gives a better estimate than your fourth, when fatigue has crept in.
- Estimate each lift separately. Squat, bench, deadlift and overhead press all respond differently to reps. Deadlifts in particular often under-estimate at higher reps because grip and lower back tire first.
- Keep the rep range low. A set of 5 predicts a max far better than a set of 15. If you only do high-rep sets, treat the result as a rough guide.
- Re-estimate every 3 to 6 weeks. Strength changes, and a stale 1RM makes every percentage wrong.
- Machines and dumbbells differ. The formulas were built on free-weight barbell lifts. Machine results are fine for tracking progress, but they do not convert to your barbell max.
If you are cutting or bulking, your estimated max will move with your body weight and energy intake. Our guide to TDEE vs BMR explains how to set calories so you can keep strength while changing weight, and the macro calculator splits that target into protein, carbs and fat.
Frequently asked questions
Which one-rep max formula is most accurate?
There is no single winner. Epley and Brzycki are the most widely used and both perform well for sets of 10 reps or fewer. Averaging the two smooths out their opposite biases and is a sensible default for most lifters.
How many reps should I use to estimate my 1RM?
Between 3 and 6 reps is ideal, and up to 10 is acceptable. The further you get from a single rep, the more your personal muscular endurance affects the answer, so error grows with every extra rep.
Is it safe to test a true one-rep max?
It can be for experienced lifters who warm up properly and use safety bars or a spotter, but it is rarely necessary. Beginners gain strength quickly on percentages from an estimated max, and avoiding true max attempts lowers injury risk. If in doubt, ask a qualified coach.
Work out your numbers in seconds
The formulas are simple enough for pen and paper, but if you want Epley, Brzycki and other estimates side by side with a full percentage table, use our free one rep max calculator. Enter the weight in kg or lb and the reps you managed, and it does the rest. You can also switch units with the kg to lb weight converter if your gym’s plates are in a different system from your programme.
Reminder: this is general information, not medical advice. Stop any lift that causes pain and seek advice from a healthcare professional.