1RM Calculator

Your one-rep max is the heaviest load you could lift once. Testing it directly carries real injury risk, so it is normally estimated from a set taken with a lighter weight. This calculator runs both the Epley formula — weight × (1 + reps/30) — and the Brzycki formula — weight × 36 ÷ (37 − reps) — and reports their average.

How to use

1. Enter the weight you actually lifted.
2. Enter how many clean reps you completed with it.
3. Read the estimated max along with each formula's individual result.
4. To set training loads, multiply the estimate by your target percentage, such as 70 or 85 percent.

When you actually need this

• Starting a programme such as 5×5 or 5/3/1 that prescribes loads as a percentage of max.
• Recording a strength baseline without attempting a true single.
• Comparing this month's numbers against a log from months ago on the same basis.
• Choosing the load for the next session.

Where the estimate breaks down

Both formulas are most reliable at low rep counts. Between one and five reps they track measured maxes closely; past ten, muscular endurance starts to dominate and the estimate drifts upward. Epley returns the higher number at high reps and Brzycki the more conservative one, so the gap between them is itself a rough measure of how much to trust the result. The estimate also assumes every rep was completed with the same technique — reps padded with bounce or a shortened range of motion produce a number you cannot actually lift. Accuracy varies by movement too, with the deadlift generally noisier than the squat or bench press.

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FAQ

What formula does 1RM Calculator use?

It uses the standard published formula for this calculation, applied exactly as written with no rounding until the final result. The inputs you provide are the only variables — there are no hidden assumptions or regional adjustments.

How accurate is the result from 1RM Calculator?

The arithmetic is exact to the precision your browser supports. Accuracy in practice depends on your inputs: an estimate built on rounded figures will itself be an estimate, so enter the most precise values you have.

Can I use this for official or financial decisions?

Treat the output as a well-calculated estimate rather than professional advice. For medical, tax, legal or lending decisions, confirm the figure with a qualified professional or the institution involved before acting on it.