Free Strength Tool · lb & kg

One Rep Max CalculatorKNOW YOUR LIMIT.
THEN BREAK IT.

This One Rep Max Calculator estimates the heaviest weight you could lift for a single rep — just enter a set you've already done. Seven proven strength formulas, one brutal number.

The Lift

Weight Lifted

Unit

Reps Performed — 5

Estimated 1RM

Average of 7 strength formulas

THE LAST REP IS WHERE THE SET BEGINS.

— Iron Law #1

TRAINING PERCENTAGES

Program your working sets off your estimated max. Percentages map to typical rep targets.

% of 1RM	Load	Reps	Focus

WHAT IS A ONE REP MAX?

Your one rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise with good form. This One Rep Max Calculator estimates that number from a set you've already completed, so you can find your max without attempting a risky all-out single.

How to use the One Rep Max Calculator

Enter the weight you lifted and choose your unit (lb or kg).
Set the number of reps you completed with that weight (best with a hard set of 1–5 reps).
Read your estimated 1RM — the average of 7 strength formulas — instantly.
Use the training percentage table to program your working sets for strength, power, or hypertrophy.

The 1RM formulas we use

Rather than rely on a single equation, this calculator averages seven peer-reviewed 1RM formulas for a more balanced estimate. For a weight w lifted for r reps:

Epley: 1RM = w × (1 + r ÷ 30)
Brzycki: 1RM = w × 36 ÷ (37 − r)
Lander: 1RM = (100 × w) ÷ (101.3 − 2.67123 × r)
Lombardi: 1RM = w × r^0.10
Mayhew et al.: 1RM = (100 × w) ÷ (52.2 + 41.9 × e^(−0.055 × r))
O'Conner et al.: 1RM = w × (1 + r ÷ 40)
Wathan: 1RM = (100 × w) ÷ (48.8 + 53.8 × e^(−0.075 × r))

Estimates are most accurate for sets of 1–5 reps and gradually lose accuracy above 10 reps, where small differences in technique and conditioning have a larger effect.

Training off your estimated max

Once you know your 1RM, you can program every set as a percentage of it: heavy singles and doubles at 90–100% build maximal strength, 70–85% drives hypertrophy and power, and 50–65% suits warm-ups, technique work, and recovery. The percentage table above does this math for you in your chosen unit.

ONE REP MAX FAQ

How accurate is a one rep max calculator?

A one rep max calculator is an estimate, typically within about 5–10% of your true max. It is most accurate when you base it on a hard set of 1–5 reps taken close to failure. The more reps you perform, the more the estimate can drift, because endurance and technique start to matter more than pure strength.

How many reps should I use for the best estimate?

For the most accurate one rep max estimate, use a challenging set of 2 to 5 reps performed with good form and close to failure. Sets above 10 reps are less reliable for predicting a true single.

Which 1RM formula is the most accurate?

No single formula is best for everyone. Epley and Brzycki are the most widely used, but each formula behaves slightly differently across rep ranges. This calculator averages seven formulas (Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, and Wathan) to smooth out the differences and give a more balanced number.

Can I use it for bench press, squat, and deadlift?

Yes. The same formulas apply to any barbell or compound lift, including bench press, back squat, deadlift, overhead press, and rows. Enter the weight and reps for that specific exercise to estimate its 1RM.

Should I actually test my one rep max?

For most lifters, estimating your one rep max is safer and good enough for programming. If you do test a true max, warm up thoroughly, use a spotter or safety bars, and only attempt it occasionally when you are well-rested.

Does the calculator work in both lb and kg?

Yes. Toggle between pounds (lb) and kilograms (kg) at any time. The calculator converts your entered weight automatically and shows your estimated 1RM and the full training-percentage table in the unit you choose.

One Rep Max CalculatorKNOW YOUR LIMIT.THEN BREAK IT.