How to Calculate Your One Rep Max (Without Testing It)

5 min read

Estimate your one rep max from a set of 2 to 10 reps: Epley is weight × (1 + reps ÷ 30), and Brzycki is weight × 36 ÷ (37 − reps). Averaging both gives a solid estimate. For example, 100 kg for 5 reps works out to about 115 kg.

Your one rep max is the heaviest weight you can lift once with good form. It is a useful yardstick for strength and for planning your training, but you don't need to grind out a risky max attempt to know it. A normal working set and a simple formula get you close enough.

What a one rep max is

Your one rep max, or 1RM, is the most weight you can lift for a single clean repetition on a given exercise. It is specific to the lift. Your squat 1RM tells you nothing about your bench press.

Why care? Many training programs prescribe weights as a percentage of your 1RM, such as 4 sets of 8 at 75 percent. Knowing your number turns those plans into real weights. It also gives you a single figure to track over months, even when the weights and reps you use change from week to week.

Estimating 1RM from a submaximal set

You can estimate your 1RM from any hard set where you stop close to failure. Two formulas are the most widely used:

To get a good input set, warm up properly, then pick a weight you think you can lift for about 3 to 8 reps. Do as many clean reps as you can, stopping when the next rep would break down your form. Use that weight and rep count in the formulas.

▸Epley: 1RM = weight × (1 + reps ÷ 30).
▸Brzycki: 1RM = weight × 36 ÷ (37 − reps).
▸Average the two for a balanced estimate.

A worked example

Say you bench press 100 kg for 5 reps. Epley gives 100 × (1 + 5 ÷ 30), which is about 117 kg. Brzycki gives 100 × 36 ÷ 32, which is 112.5 kg. The average is about 115 kg, a sensible estimate of your 1RM.

The two formulas agree closely at low reps and drift apart as reps rise. Estimates are most reliable from sets of about 3 to 8 reps. Above roughly 12 reps, endurance plays a bigger role and the number becomes a rough guide. The set also needs to be genuinely hard. A set of 5 you could have done for 10 will badly underestimate your max.

Using percentages to plan training

Once you have an estimated 1RM, percentages give you working weights for different goals. These are common ranges and the reps you can typically do at each:

▸85 to 95 percent: about 2 to 5 reps. Heavy strength work.
▸75 to 85 percent: about 5 to 8 reps. Strength and size.
▸65 to 75 percent: about 8 to 12 reps. The main range for building muscle.
▸50 to 65 percent: about 12 to 20 reps. Technique, volume and endurance.
▸40 to 60 percent: warm-up sets before your working weight.

A sample week built from your 1RM

Using the 115 kg bench example, here is how percentages turn into a plan across two upper body days. Day one, heavier: bench press 4 sets of 5 at 80 percent, about 92.5 kg. Day two, lighter: bench press 3 sets of 10 at 67 percent, about 77.5 kg, plus incline dumbbell press 3 sets of 12.

Round to the nearest weight you can actually load. Each week, try to add a rep or a small amount of weight. Re-estimate your 1RM every few weeks from a hard set, so your percentages keep pace with your strength.

These percentages are guides, not orders. On a day when you slept badly or feel run down, the weights will feel heavier, and that is normal. Drop the load a little and keep your form clean. Your log will show the overall trend climbing even with an off day here and there.

Safety: you don't need to test a true max

Testing a true 1RM is tiring, carries more injury risk and needs a spotter or safety pins, plus solid technique under very heavy load. For most people training for health, muscle or general strength, it adds little that an estimate doesn't give you.

If you do want to test a max, do it rested, warm up thoroughly with gradually heavier singles, use safeties on squat and bench, and stop at a weight you can lift with clean form. Never test a max on a lift you are still learning. If you have an injury or a heart or blood pressure condition, check with a doctor before any maximal lifting.

Calculate it in seconds

The free one rep max calculator on SSS Workout Assistant does the math for you. Enter the weight and reps from any recent set, in kilograms or pounds, and it shows the Epley and Brzycki results, their average, and a percentage table for planning your working weights. If you log workouts in the app, its progress charts also track your estimated one rep max over time.

FAQ

How accurate is a one rep max calculator?

Usually within a few percent when the set is hard and in the 3 to 8 rep range. Accuracy drops above about 12 reps, and people with more endurance or more strength may find the estimate a little high or low. Use it as a planning guide.

How often should I check my one rep max?

Every 4 to 8 weeks is plenty. Estimate it from a hard set during a normal session rather than testing a true max.

Which formula is better, Epley or Brzycki?

Neither is clearly better for everyone. They are very close at low reps; Epley tends to give a slightly higher number as reps increase. Averaging both is a simple way to balance them.

Can I estimate 1RM for dumbbell or machine exercises?

Yes, the formulas work on any lift. They are most useful for big compound lifts, though. For small isolation exercises, tracking reps and weight directly is more practical.

What is a good one rep max for my body weight?

It varies widely with age, sex, training history and the lift. Rather than comparing to others, compare your estimate to your own from a few months ago. Steady improvement is what matters.

Put it into practice

SSS Workout Assistant turns these principles into a free weekly routine built around you — then tracks every set and reminds you to train so you actually keep it.

Start training free