Why estimate your 1RM instead of testing?
Testing a true 1-rep max is useful — once or twice a year, when you're peaked, fresh, and have a spotter. The other 50 weeks, you don't need to. An estimated 1RM from a working set tells you what to load on every percentage-based set you'll ever program, with under 5% error for sets in the 3–6 rep range (Source: LeSuer et al., The accuracy of prediction equations for estimating 1-RM performance, J Strength Cond Res, 1997).
The two formulas worth knowing
Dozens of 1RM equations exist. Two are responsible for nearly every result you'll see online.
Epley
1RM = weight × (1 + reps/30)
Example: 225 lb × (1 + 5/30) = 262.5 lb
Brzycki
1RM = weight × 36 / (37 − reps)
Example: 225 lb × 36 / (37 − 5) = 253.1 lb
Which is more accurate? Epley tends to over-estimate slightly above 5 reps and Brzycki tends to under-estimate above 10 reps (Source: LeSuer et al., 1997). For sets of 3–6 reps both are within ~3% of measured 1RMs. The calculator below averages them so you don't have to choose.
How to perform the test set
To get a useful estimate, the rep count must be honest. That means:
- Warm up properly. 3–5 progressive sets up to your working load.
- Pick a load you can do for 3–6 honest reps, with 1 rep left in the tank (RIR 1). Do not grind the last rep. Test sets with form breakdown over-estimate 1RM by 5–15%.
- Use the same equipment (bar, plates, shoes) you'd use for a real attempt.
- Use a spotter for any compound test set above ~80% of your training max.
- Run the test for the lift you care about — squat, bench, deadlift, overhead press. The estimate is only valid for that exact lift.
Why higher rep ranges break the formula
Both Epley and Brzycki are reliable in the 2–8 rep window. Past that, individual differences in slow-twitch fiber dominance, neuromuscular efficiency, and pacing cause errors of 10% or more (Source: Reynolds et al., Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry, J Strength Cond Res, 2006). If the only data you have is a 15-rep set, treat the result as a rough ceiling and re-test in the 3–6 range when possible.
How to use a 1RM in programming
The whole point of estimating 1RM is loading other sets correctly. Common percentage prescriptions:
| Goal | % of 1RM | Reps |
|---|---|---|
| Strength | 80–95% | 1–5 |
| Hypertrophy | 65–80% | 6–12 |
| Muscular endurance | 50–65% | 12–20 |
| Power / speed | 50–70% (compensatory accel.) | 1–5 (fast intent) |
A working program weaves all three. Strength blocks typically prescribe loads as a percent of 1RM. Hypertrophy blocks usually prescribe RPE or reps-in-reserve, but starting loads still come from your 1RM estimate.
The free workout templates linked below pre-fill these percentages so you can plug your number in and run.
When to re-estimate
- Beginners (under 1 year of consistent training): every 4 weeks.
- Intermediates: every 6–8 weeks.
- Advanced lifters: every 8–12 weeks, or whenever a percentage-based session feels easier than expected for two sessions in a row.
Common mistakes
- Using a half-ROM set. A high-bar quarter squat at 405 lb tells you nothing about your real squat 1RM.
- Using a near-max grindy set. RIR 0–1 reps with form breakdown inflate the estimate by double digits.
- Estimating from machine work. Machines change the strength curve. A leg-press 1RM estimate doesn't translate to back squat.
- Estimating once and never updating. Your 1RM moves. Re-test on schedule.
How Fitly automates 1RM tracking
If you log your sets in Fitly, you don't need to do this math at all:
- Every working set automatically updates your estimated 1RM.
- Smart Coach uses your live 1RM to set loads on percentage-based programs.
- Personal records and progress charts show your strength trajectory over time.
Open the 1RM calculator Get the workout templates