How to Estimate a 1RM Without Testing for One

Dated caveat. The Epley (1985), Brzycki (1993), and Lombardi (1989) formulas are still the workhorses despite pre-dating modern sports science. Their accuracy is unchanged; there's no newer formula that systematically outperforms them.

The three formulas

Epley:     1RM = weight × (1 + reps/30)
Brzycki:   1RM = weight × 36 / (37 − reps)
Lombardi:  1RM = weight × reps^0.10

Example: 100 kg × 5 reps (taken to failure):

  Epley:     100 × (1 + 5/30) = 116.7 kg
  Brzycki:   100 × 36/32       = 112.5 kg
  Lombardi:  100 × 5^0.10      = 117.5 kg

Average:   ~115 kg (all within 4%)

The three formulas diverge most at low rep counts (2–3 reps) and converge in the 4–6 rep range. Brzycki is most conservative; Epley and Lombardi are slightly more aggressive. For general use, average them or pick one and stick with it. The 1RM Calculator returns all three and the mean so you can see the spread.

When the formulas work well

All three formulas are accurate when:

• The rep count is between 2 and 6.
• The set was taken to actual failure (RPE 9.5–10) or within ~1 rep of it.
• The movement is a compound barbell lift (squat, bench, deadlift, overhead press).
• The lifter has at least 6 months of consistent training.

A 225 lb × 5 rep set to failure on bench press gets you a 1RM estimate in the 258–263 lb range depending on formula. That number is within 5 lb of what you'd actually hit on a max attempt.

When the formulas break

• Above 10 reps. The rep-to-1RM relationship becomes increasingly nonlinear. A set of 20 at a given weight doesn't predict 1RM well at all.
• Sets not taken to failure. If you stopped at RPE 7 with 3 reps in reserve, you need to subtract 3 from the reps your weight could actually produce — otherwise you're treating RPE 7 as if it were RPE 10.
• Isolation lifts. Curls, lateral raises, and similar. Formulas were calibrated on compounds; they systematically over-predict for isolations.
• Novices. Technique noise swamps the strength signal, so the estimate doesn't match what they could actually max out at.

RPE-based estimation

For anyone with reliable RPE calibration, the RPE-to-percentage lookup is more useful than rep-based formulas^[2]. An RPE 9 set of 5 corresponds to approximately 86% of 1RM; an RPE 8 set of 5 to approximately 82%; an RPE 7 set of 5 to approximately 79%.

Quick RPE ↔ percentage-of-1RM table (for 5-rep sets):

RPE 10    100% of a 5RM       ~86% of 1RM
RPE 9     95% of a 5RM        ~82% of 1RM
RPE 8     90% of a 5RM        ~79% of 1RM
RPE 7     85% of a 5RM        ~75% of 1RM

Example: you do 100 kg × 5 at RPE 8. Your 1RM is approximately 100 / 0.79 ≈ 127 kg.

The RPE to Percentage Converter provides the full lookup table for 1-to-10-rep sets at every RPE. This is the most practical way to estimate 1RM in training without ever going to RPE 10.

The rep-range estimation lookup

If you know what weight you can do for a given rep count at roughly RPE 9:

Reps to RPE 9   Percentage of 1RM
─────────────────────────────────
  1             100% (by definition)
  2              95%
  3              92%
  4              89%
  5              86%
  6              83%
  8              78%
 10              73%
 12              68%
 15              62%

Use: if your best-controlled set of squats is 140 kg × 3 at RPE 9, your 1RM is approximately 140 / 0.92 ≈ 152 kg.

Practical workflow: updating your 1RM

1. Do a top set at RPE 8–9 on your main lift during each mesocycle (e.g. every 4–6 weeks).
2. Record: weight × reps × RPE.
3. Run the calculation (RPE method preferred).
4. Set percentages for the next block off this updated estimate.

This is the intermediate-lifter's equivalent of a periodic 1RM test, without the injury risk and CNS cost of actually grinding a true max.

Formula agreement across the rep range

A head-to-head comparison of all three formulas at given weight-and-rep combinations:

Weight × reps     Epley    Brzycki    Lombardi    Spread
─────────────────────────────────────────────────────────
100 × 1            100       100        100          0
100 × 2            107       106        107          1
100 × 3            110       109        110          1
100 × 5            117       113        118          5
100 × 8            127       121        127          6
100 × 10           133       128        132          5
100 × 12           140       133        135          7
100 × 15           150       143        142          8

Formulas agree tightly at 1–3 reps and fan out at higher rep counts. At 15 reps, the 8 kg spread exceeds the reliability of any individual formula. This is why high-rep-based estimates aren't useful for programming.

Using percentages from the estimate

Once you have a reliable 1RM estimate, programming percentages for different goals:

Goal                   % 1RM       Reps     Sets     RPE cap
────────────────────────────────────────────────────────────
Hypertrophy (light)    65–72%      8–12     3–4      7–8
Hypertrophy (medium)   72–80%      5–8      3–4      8
Hypertrophy (heavy)    80–85%      3–5      4–5      8
Strength (general)     80–87%      3–5      4–6      8–9
Peak strength          87–92%      1–3      3–5      9
Testing                92–100%+    1        1         10

Percentages scale reliably when the 1RM estimate is reliable — i.e. within ±3% of the true value. When the estimate is off by 5%+, percentages shift enough to change the training effect. Re-estimate periodically.

Meet-prep exception

Two to three weeks before a powerlifting meet, you should have an actual heavy single on record — a 95%+ opener simulation or an RPE 9 single. This anchors your attempt selection^[3] better than a rep-based estimate. Outside of meet prep, there's no reason to test a grinding 1RM.

Safety for any heavy test

• Squat: Set safety bars / J-hooks. Lift in a power rack if available. Use a competent spotter.
• Bench: Always use a spotter for anything above 85% 1RM, or use safety bars set to unlock position.
• Deadlift: No spotter available; the risk is back strain, not being crushed. Be conservative if form is breaking down.
• Overhead press: Use a power rack. Catch bars set 2–3 inches above your heaviest starting position.

The Plate Loading Calculator helps avoid the other common gym accident: loading the wrong plate arrangement and surprising yourself under the bar.

For bodybuilders and general lifters

Most hypertrophy work doesn't require an accurate 1RM. Percentage-based templates for hypertrophy are less precise than percentage-based templates for strength because the relationship between load and hypertrophic response is wider. If your goal is muscle size, an RPE-based estimate updated every couple of months is sufficient. Don't obsess about the precise 1RM number.

Worked example: updating three 1RMs without a test session

An intermediate lifter completes top sets across a mesocycle and wants to reset training percentages for the next block without a dedicated 1RM test day.

Lift       Top set          RPE   Method         Estimated 1RM
───────────────────────────────────────────────────────────────
Squat      170 kg × 3       8     RPE (89% of1RM) 170 / 0.89 = 191 kg
                            —     Epley (reps 3)   170 × (1+3/30)= 187 kg
                            —     Brzycki (reps 3) 170 × 36/34   = 180 kg
                            Mean                                 ~186 kg

Bench      120 kg × 5       9     RPE (82% of1RM)  120 / 0.82 = 146 kg
                            —     Epley            120 × 1.167  = 140 kg
                            —     Brzycki          120 × 36/32  = 135 kg
                            Mean                                 ~140 kg

Deadlift   200 kg × 2       8.5   RPE (~91% of1RM)200 / 0.91 = 220 kg

Note the spread: on squat, Brzycki reads 11 kg below the RPE-based estimate because Brzycki is the most conservative formula at low reps^[1]. Programming percentages for the next block off the mean gets you inside the ±3–5% error band of any single formula. Training 5×3 at 80% off a 186 kg squat estimate = 149 kg — a defensible working weight that won't be systematically under- or over-loaded.

Common failure modes

• Estimating from sets that weren't close to failure. A 100 kg × 8 set at RPE 7 (3 RIR) is not a "rep-max" — it's an 8-rep set that could have been 11. Formulas treating it as RPE 10 overstate true 1RM by 8–12%.
• Using high-rep sets as the input. At 15+ reps, Epley, Brzycki, and Lombardi spread by 8+ kg and all over-predict relative to what you'd actually grind out on a max attempt. Use sets of 2–6 reps for estimation, nothing higher.
• Mixing formulas across lifts. Pick one method (RPE-based, or averaged-formula) and apply it consistently. Using Epley on squat and Brzycki on bench produces incomparable numbers across lifts.
• Testing a true 1RM without meet-prep context. NSCA guidance^[3] treats actual maximal testing as a trainable event, not a weekly tool. Injury risk scales with proximity to failure, and CNS cost cuts into the next several sessions. Estimate routinely; test rarely.

Connects to

• How to Use RPE for Training — RPE calibration underpins RPE-based 1RM estimation.
• How to Structure a Powerlifting Meet — where a known 1RM actually matters.
• Evidence-Based Programming — using percentages correctly once you have a reliable 1RM.

Tools: 1RM Calculator, RPE to Percentage Converter, Plate Loading Calculator.