1RM Calculator

Estimate your one-rep max from any rep range, compare six standard formulas, and get a working-weight table for programming.

Estimated 1RM

260.52 lb

Average of 6 formulas

Conservative

253.13 lb

Lowest estimate

Median

262.41 lb

Middle estimate

Aggressive

267.77 lb

Highest estimate

Formula	Estimated 1RM
Epley	262.5 lb
Brzycki	253.13 lb
Lombardi	264.29 lb
Wathan	262.31 lb
O'Conner	253.13 lb
Mayhew	267.77 lb

Working percentages from your 1RM

Reps	% of 1RM	Working weight
1	100%	260.52 lb
2	95%	247.49 lb
3	93%	242.28 lb
4	90%	234.47 lb
5	87%	226.65 lb
6	85%	221.44 lb
7	83%	216.23 lb
8	80%	208.42 lb
9	77%	200.6 lb
10	75%	195.39 lb
11	70%	182.36 lb
12	67%	174.55 lb

The six formulas

This calculator runs all six widely-cited 1RM formulas and surfaces the average so you don't have to pick a favorite. The formulas all degrade past about 10 reps — for higher rep sets, use the conservative estimate.

Epley (1985): 1RM = w · (1 + r/30)
Brzycki (1993): 1RM = w · 36 / (37 − r)
Lombardi (1989): 1RM = w · r^0.10
Wathan (1994): 1RM = 100w / (48.8 + 53.8 · e^−0.075r)
O'Conner (1989): 1RM = w · (1 + 0.025r)
Mayhew (1992): 1RM = 100w / (52.2 + 41.9 · e^−0.055r)

How to use your estimate

Program off the average — it smooths out the quirks of any single formula.
Use the conservative number when you haven't tested in months or are returning from a break.
Re-estimate every 4–6 weeks from your heaviest recent set. The ProLoad app tracks this automatically and surfaces your strongest set per exercise.
Round to plate increments before loading the bar — see our plate calculator.

Use this as an API

Build with the Proload API

Send weight + reps as JSON, get all six formulas plus the average and a percent table back. 1,000 requests/day free.

POST https://api.proload.online/v1/one-rep-max

API docs Get a key

Frequently asked questions

How accurate is a 1RM calculator?

For sets of 1–8 reps, predicted 1RM is typically within 5% of an actual tested max for most lifters. Accuracy degrades past 10 reps because rep-out endurance varies by exercise and individual. Use the average of multiple formulas for a robust estimate.

Which formula is the most accurate?

No single formula wins across all lifts. Epley and Brzycki tend to be the most cited in research. Most strength coaches average several formulas to get a working estimate — which is what this tool does by default.

Should I program my training off of an estimated 1RM?

Yes — and most lifters do. Use the conservative estimate for compound lifts you have not maxed recently, and re-test only when peaking. The percent table below your estimate gives you working weights for sets of 1 through 12 reps.

Does this tool save my data?

No. All calculations happen in your browser. If you want a full training history with automatic PR detection, install the free ProLoad app.

Can I use this in my own app?

Yes — every calculator on this page is also available as a JSON API at api.proload.online. The free tier covers 1,000 requests per day.

1RM Calculator

How to use your estimate

Build with the Proload API

Frequently asked questions

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RPE ↔ %1RM