Your one-rep max (1RM) is the most weight you can lift once with good form. Many strength programs prescribe loads as a percentage of it, but testing it directly is tiring and carries some risk. This calculator estimates it from a lighter set you have already done, using seven published equations, and turns the result into a loading chart.
How to use the one-rep max calculator
- Choose pounds or kilograms.
- Enter the weight lifted, including the bar.
- Enter the reps completed in a hard set, ideally one you finished with no more than one or two reps left in reserve.
- Pick the main formula or use the average of all seven.
- Use the percentage table for training loads, rounded to the nearest 5 lb or 2.5 kg for loading the bar.
One-rep max formulas
With w = weight lifted and r = repetitions:
The comparison table also shows O’Conner, Lander, Mayhew and Wathan. A single rep is treated as your 1RM in every formula.
Worked example
You bench press 225 lb for 5 reps:
Epley: 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lb
Brzycki: 225 × 36 ÷ 32 = 225 × 1.125 = 253.1 lb
Lombardi: 225 × 50.10 = 225 × 1.1746 = 264.3 lb
The estimates span about 11 lb. A 262.5-lb max means 80% is 210 lb and 70% is about 185 lb for loading.
Percentage of 1RM chart
The table under the result lists loads from 100% down to 50% of your estimate, with the reps you could typically complete at each one (the average of the inverted Epley and Brzycki equations). As a rough guide:
| % of 1RM | Typical reps | Common use |
|---|---|---|
| 95–100% | 1–2 | Maximal strength, peaking |
| 85–90% | about 4–6 | Heavy strength work |
| 75–80% | about 8–10 | Strength and muscle growth |
| 65–70% | about 12–15 | Muscle growth, volume |
| 50–60% | about 18–25 | Warm-ups, technique, speed work |
Getting a reliable estimate
Use a recent, honest set
The formulas assume the set was close to failure. If you stopped with five reps in the tank, the estimate will be too low. Use a set from the last week or two so it reflects current strength.
Expect individual differences
People with more fast-twitch muscle fibers often manage fewer reps at a given percentage than the formulas predict, while endurance-trained lifters manage more. If your real max and estimate differ, note the gap and adjust future estimates.
Re-estimate as you progress
As strength rises, update the 1RM every few weeks rather than waiting for a test day. Pair heavier training with enough protein (the protein intake calculator gives a daily target) and see what a session burns with the calories burned calculator. To switch between units, use the kilograms to pounds converter.
Informational only — not medical advice. Heavy lifting raises blood pressure sharply during the effort; people with heart disease, uncontrolled hypertension or recent injuries should get clearance before maximal training.
Frequently asked questions
Which one-rep max formula is the most accurate?
None is best for everyone. Epley and Brzycki agree closely at about 3–6 reps and are the most widely used. Brzycki tends to give lower estimates at higher reps, while Epley and Lombardi run higher. Averaging several formulas smooths out their quirks.
How many reps should I use to estimate 1RM?
Sets of about 3 to 8 reps taken close to failure give the best predictions. Beyond about 10 reps, endurance plays a bigger role and the formulas disagree more.
Is it safe to test a true one-rep max?
It can be for experienced lifters with good technique, a thorough warm-up and a spotter or safety pins. Beginners usually get the information they need from an estimate without the injury risk of a maximal attempt.
Do the formulas work for every exercise?
They were developed mostly for the bench press and squat. They work reasonably for other compound barbell lifts but are less reliable for machines, isolation exercises and bodyweight movements.