What is a one-rep max?

Your one-rep max (1RM) is the heaviest weight you can lift for a single, full repetition of an exercise. It's the standard yardstick for maximal strength and the reference point for percentage-based training.

How accurate are 1RM formulas?

Estimates from a set of 1–10 reps are usually within a few percent of a true tested max. Accuracy is best at low rep counts (1–5) and drifts as reps climb, because endurance and technique start to dominate.

Epley vs Brzycki — which is better?

Neither is universally best. Epley tends to read slightly higher at moderate-to-high reps, Brzycki slightly lower. Averaging the two — as this calculator does — smooths out their individual quirks.

How do I use my 1RM to program training?

Pick a percentage of your 1RM that matches your goal: roughly 85–100% for strength (1–5 reps), 70–85% for hypertrophy (6–12 reps). The chart in the calculator gives the working weight for each rep target.

Is it safe to test a true 1RM?

Testing a genuine max carries real injury risk and demands a thorough warm-up, solid technique, and a spotter or safety bars. Estimating from a comfortable multi-rep set is a safer way to track progress for most lifters.

One-Rep Max Calculator

This one-rep max calculator estimates the heaviest weight you could lift for a single rep, using the Epley and Brzycki formulas, and builds a percentage-of-1RM chart to set your working weights.

1RM · Estimate

Weight lifted (kg)

Units

Reps performed (1–12)

114.6 kgestimated one-rep max

Epley

116.7 kg

Brzycki

112.5 kg

Percentage of 1RM

Reps	%1RM	Weight
1	100%	114.5 kg
2	95%	109 kg
3	93%	106.5 kg
4	90%	103 kg
5	87%	99.5 kg
6	85%	97.5 kg
7	83%	95 kg
8	80%	91.5 kg
9	77%	88 kg
10	75%	86 kg
11	72%	82.5 kg
12	70%	80 kg

Average of the Epley and Brzycki formulas. An estimate — warm up and use a spotter before any heavy attempt.

How it works

A one-rep max (1RM) is the most weight you can move for one full repetition. Rather than testing it directly, you can estimate it from a lighter set taken close to failure. This tool uses two long-standing load–rep equations and reports their average:

Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)

At a single repetition both formulas simply return the weight lifted. As reps rise, the estimates climb to account for the strength reserve a sub-maximal set leaves on the table.

Worked example

Suppose you bench 100 kg for 5 reps:

Epley = 100 × (1 + 5 ÷ 30) = 116.7 kg
Brzycki = 100 × 36 ÷ (37 − 5) = 112.5 kg
Average ≈ 114.6 kg — your estimated 1RM

From there, 80% of 114.6 kg ≈ 91.5 kg is a sensible hypertrophy-range working weight for sets of about 8.

Percentage-of-1RM training guide

Typical relationship between a percentage of your 1RM and the reps you can expect to complete:

% of 1RM	Reps
100%	1
95%	2
93%	3
90%	4
87%	5
85%	6
83%	7
80%	8
77%	9
75%	10
72%	11
70%	12

These are population averages; your own rep-to-percent profile varies by exercise and training experience.

Putting it to use

Once you have a 1RM, lean on it to program loads, then pressure- test the number with the RPE Calculator and compare your lifts against the Strength Standards Calculator.

Frequently asked questions

What is a one-rep max?: Your one-rep max (1RM) is the heaviest weight you can lift for a single, full repetition of an exercise. It's the standard yardstick for maximal strength and the reference point for percentage-based training.
How accurate are 1RM formulas?: Estimates from a set of 1–10 reps are usually within a few percent of a true tested max. Accuracy is best at low rep counts (1–5) and drifts as reps climb, because endurance and technique start to dominate.
Epley vs Brzycki — which is better?: Neither is universally best. Epley tends to read slightly higher at moderate-to-high reps, Brzycki slightly lower. Averaging the two — as this calculator does — smooths out their individual quirks.
How do I use my 1RM to program training?: Pick a percentage of your 1RM that matches your goal: roughly 85–100% for strength (1–5 reps), 70–85% for hypertrophy (6–12 reps). The chart in the calculator gives the working weight for each rep target.
Is it safe to test a true 1RM?: Testing a genuine max carries real injury risk and demands a thorough warm-up, solid technique, and a spotter or safety bars. Estimating from a comfortable multi-rep set is a safer way to track progress for most lifters.

Related calculators

Disclaimer. This is an estimate, not a tested maximum. Always warm up thoroughly and use a spotter or safety equipment before attempting a heavy single. Not medical advice.