One Rep Max Calculator

What a one-rep max is — and why you estimate it

Your one-rep max (1RM) is the heaviest weight you can lift for a single, full repetition of an exercise. It is the reference point for nearly all strength programming: percentages of your 1RM tell you how heavy to go for strength, hypertrophy, or technique work.

The problem is that actually testing a true 1RM is tiring, technically risky, and something you cannot do every week. So instead of maxing out, you estimate your 1RM from a set you already perform — say 100 kg for 5 reps — using a validated formula. The estimate updates every time you log a heavier set, so your training weights stay calibrated to your current strength rather than where you were a month ago.

The formulas this calculator uses

There are several published 1RM equations. This tool uses the two most trusted for moderate rep ranges and averages them — exactly what the LiftZone Workouts app does:

• Epley: 1RM = weight × (1 + reps ÷ 30)
• Brzycki: 1RM = weight ÷ (1.0278 − 0.0278 × reps)
• LiftZone estimate: the average of the Epley and Brzycki results

For example, a set of 100 kg × 5 reps gives an Epley estimate of about 117 kg and a Brzycki estimate of about 113 kg — an averaged 1RM of roughly 115 kg. Averaging matters because Epley tends to read slightly high and Brzycki slightly low as reps increase; together they cancel out much of that bias.

Turning your 1RM into training weights

Once you know your 1RM, the chart above converts it into a target weight for every rep count. Lower reps at higher percentages build maximal strength; moderate reps around 70–80% drive most of your muscle growth; higher reps build work capacity. Plan your heavy days and your back-off sets straight off the table instead of guessing.

If you want to know how many sets to do at those weights each week, use the training volume calculator for evidence-based MEV/MAV/MRV set targets per muscle.

Methodology & accuracy

Estimated 1RMs are most reliable from sets of 5 reps or fewer taken close to failure; accuracy decreases as reps rise because fatigue, technique, and rep cadence introduce more variation. The Epley and Brzycki equations are long-established in strength science and are widely used by coaches and lifting apps. These are the same equations and the same percentage table built into LiftZone Workouts, which recomputes your estimated max from your real logged sets after every session.

Note: estimates are guidance, not a guarantee — always warm up properly and use a spotter for heavy singles. Last reviewed June 2026.

Frequently asked questions

Which 1RM formula is most accurate?
For most lifters in the 1–10 rep range, the Epley and Brzycki formulas land within a few percent of each other. Averaging them — what this calculator and the LiftZone app do — smooths out their individual bias. Accuracy is highest at low reps (1–5) and drifts as reps climb, because fatigue and technique vary more on high-rep sets.

How many reps give the most accurate estimate?
Use a hard set of about 5 reps or fewer, taken close to failure. The fewer the reps, the more accurate the estimate. Sets above 10–12 reps tend to overestimate your true one-rep max.

What is the %1RM chart for?
It converts your estimated 1RM into target weights for every rep range, so you can load strength work (about 85–100%), hypertrophy work (about 70–80%) and back-off sets correctly instead of guessing.

Does RPE change the estimate?
Yes. If a set was not taken to failure, your true max is higher than the raw numbers suggest. Entering an RPE adds the estimated reps in reserve (10 minus RPE) before applying the formula, giving a more honest 1RM.

Should I test a true one-rep max instead?
Occasionally, with full warm-ups and a spotter, experienced lifters can test a true max. But an estimate from your normal working sets is safer, repeatable, and updates every session — which is how LiftZone keeps your prescribed weights calibrated to your current strength.