How to Estimate Your 1RM From a Rep Set

Your one-rep max (1RM) is the heaviest load you can lift once with good form. Every percentage in a strength plan points back to it. If the 1RM is wrong, every load in the plan is wrong too.

You do not need to grind out a true max to get a useful number. A hard set of a few reps gives you a reliable estimate. This guide shows you how to calculate it, which reps to use, and when a real test is worth it.

Why an estimated 1RM works

A rep set and a single are two points on the same strength curve. If you know how many reps you can do with a load, you can predict the load you could do for one. That is all a 1RM formula does.

The research supports this approach. Reynolds and colleagues tested 1, 5, 10 and 20RM loads on the bench press and leg press in 70 adults. They found that the 5RM gave the most accurate prediction of the true 1RM.

"Data reveal that no more than 10 repetitions should be used in linear equations to estimate 1RM for the LP and CP actions."

Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. J Strength Cond Res, 2006. PubMed

The practical rule is simple. Use a set of 2 to 10 reps, and prefer 3 to 5. The fewer the reps, the closer the set is to a true single, and the smaller the error.

The two formulas to know

Most calculators use one of two equations. Both take the weight you lifted (w) and the reps you completed (r).

• Epley: 1RM = w × (1 + r / 30)
• Brzycki: 1RM = w × 36 / (37 − r)

A worked example

Say you squat 100 kg for 5 clean reps.

• Epley: 100 × (1 + 5 / 30) = 116.7 kg
• Brzycki: 100 × 36 / 32 = 112.5 kg

The two answers sit about 4 kg apart. Below 5 reps the formulas agree closely. At 10 reps they spread further, which is one more reason to use lower rep sets.

When in doubt, take the lower number. A slightly low reference max keeps your working sets crisp. A high one turns planned sets of 5 into grinders.

How accurate are the formulas?

Accuracy is good when the set is close to failure and the reps stay low. A study by McNair and colleagues compared 12 prediction equations against measured 1RMs in adults with knee osteoarthritis. For knee extension, the best equations, including Brzycki and Epley, had typical errors between 3% and 4%. For the knee press the best equations landed at 5.9 to 6.3%.

For a 150 kg lifter, a 4% error is about 6 kg. That is close enough to set training loads. It is not precise enough to pick a meet opener.

How to run an estimate set

Treat the estimate set like a short test. The quality of the input decides the quality of the number.

1. Warm up fully. Work up through 3 to 4 lighter sets of falling reps.
2. Pick a load you can lift 3 to 5 times. Aim for a set that ends with zero or one rep left in the tank.
3. Count only clean reps. A rep with broken form or partial depth does not count.
4. Use one lift per estimate. A max for back squat is not a max for front squat or pause squat.
5. Record the date. An estimate is a snapshot. It goes stale after a training block.

If the set goes past 10 reps, the load was too light. Rest 5 minutes, add weight, and try again on another day if you are tired.

Estimate or test a true max?

A true 1RM test is also reliable when you run it well. A systematic review by Grgic and colleagues pooled 32 studies with 1,595 participants. It found a median coefficient of variation of 4.2%, and 92% of the reliability scores (ICCs) were 0.90 or higher.

So both methods work. The choice depends on your goal and your skill with heavy singles.

Estimate when:

• You are new to a lift and still learning to brace under heavy load.
• You train a variation, such as a close-grip bench or a front squat, that you never max.
• You want a fresh number mid-block without a full test day.
• You use percentages for volume work in the 65 to 80% range, where a small error matters less.

Test a true single when:

• You compete, or you plan to, and need a real opener reference.
• You train in the 90% and above range often.
• Your estimates from different rep counts disagree by more than 5%.

Many lifters do both. They test a true single on the main lift once or twice a year and estimate everything else.

Set a reference max for each lift you choose

On strengthbuild.ing you build a plan around the lifts you pick. Each of those lifts needs its own reference max. Do not assume two movements share a max.

A practical setup looks like this:

• Main lifts: squat, bench press, deadlift, or overhead press, each from a 3 to 5 rep estimate or a tested single.
• Variations: an estimate from a recent rep set on that exact variation.
• Accessories: no max needed. Program these by reps and effort.

Re-estimate after every 4 to 8 week block. A good block can add 2 to 5% to a reference max. An old number means your percentages stop matching how strong you are.

A sample estimate week

Use one session to refresh two maxes. Keep it short.

Lift	Warm-up	Estimate set	Back-off
Squat	4 sets, 8 to 2 reps	1 × 3 to 5 at RPE 9	2 × 5 at 80% of new estimate
Bench press	4 sets, 8 to 2 reps	1 × 3 to 5 at RPE 9	2 × 5 at 80% of new estimate

Plug each estimate set into Epley or Brzycki. Round the result down to the nearest 2.5 kg. That number is your new reference max.

Build it in the free builder

Open the free program builder and add each lift you plan to train. Enter a reference max for every main lift and every variation you want to load by percentage. Use the rounded estimate from your 3 to 5 rep set.

Then set your working rows as %1RM, for example 5 sets of 5 at 75 to 80%. The builder fills each load from the max you entered. Want a head start? Pick a plan from the starter programs and swap in your own lifts and maxes.