What this calculator does
It estimates your one-rep max from a weight you lifted for a given number of reps. It shows both the Epley and Brzycki results, because they disagree slightly and the range is more honest than one decimal place.
A 1RM is the most weight you can lift once with good technique. Testing it directly is stressful and carries risk, so an estimate from a hard set is often enough.
The formulas
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)Both are most reliable at 10 reps or fewer. At 15–20 reps the estimate drifts, because the set is limited by endurance and technique as much as strength.
A worked example
100 kg for 5 reps:
- Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg
- Brzycki: 100 × 36 ÷ 32 = 112.5 kg
The range is 112–117 kg. Use the lower end for conservative training percentages.
How to use it
A common approach is to train volume at 65–80% of 1RM, intensity at 80–90%, and only rarely go above 90%. The estimate is a planning tool; it is not a target to chase every session.
What this calculator does not do
It does not test your true maximum or replace a coach. It does not account for technique breakdown, equipment differences or fatigue. Do not attempt a maximal lift without a warm-up and a spotter, and stop if form fails.
Common training percentages
Once you have an estimate, percentages are easier to plan: 65% for technique work, 75% for volume, 85% for strength, 90%+ for peaking. These are conventions, not rules; adjust for how the set actually feels. Recalculate after a training block rather than every session. The estimate is only as good as the set you used.
Use the lower estimate for a new training block.
Frequently asked questions
How accurate is an estimated 1RM?
Reasonably accurate when the set is 10 reps or fewer. Above that, fatigue and technique change the result more than the formula. For a competition or a programme test, use an actual tested 1RM.
Why do Epley and Brzycki disagree?
They are different curve fits to different data. The two estimates usually land within a few percent of each other at 5–8 reps. Treat the range, not a single decimal, as the answer.
Should I test my real 1RM?
Only with good technique and a spotter, after a proper warm-up. A true 1RM is a maximal lift and carries injury risk. For most training, an estimate from a hard set of 3–5 is enough.
How do I use the number?
As a reference for training percentages — for example, 70–80% for volume work. Recalculate after a few weeks rather than treating the number as permanent.