One engine for every page

All the maths lives in a single JavaScript file that every calculator loads. The bench press, squat, deadlift and homepage calculators all call the same functions, so the same set always gives the same answer on every page. The maths runs in your browser. We never receive the numbers you type.

Which 1RM formulas do you use?

In each formula, w is the weight lifted and r is the number of reps completed.

McGlothin: the McGlothin equation, 100 × w / (101.3 − 2.67123 × r), is the same as Lander’s, so we do not show it as a separate row.

One rep: when you enter 1 rep (with no reps in reserve), every formula returns the weight itself. Some equations would otherwise add a few percent to a single, which makes no sense.

How do you pick the headline number?

By default the headline 1RM is the plain average of the seven formulas. Under it we show the lowest and highest estimate so you can see the uncertainty. In Coach mode you can choose any single formula instead. We warn you when the effective reps are above 10, and we do not accept sets above 20 reps.

How does the RPE adjustment work?

We use the reps-in-reserve (RIR) version of the RPE scale described by Zourdos and colleagues (2016) and Helms and colleagues (2016). RPE 10 means no reps left, RPE 9 means one rep left, RPE 8 means two, and so on, with half steps allowed. We convert RPE to RIR (RIR = 10 − RPE), add those reps to the reps you did, and estimate the 1RM from that total. For example, 100 × 5 at RPE 8 is treated like 100 × 7 to failure.

How do you work out rep maxes and percentages?

Each formula can be rearranged to give the weight for any number of reps from a 1RM. For rep maxes we average those seven rearranged formulas. To show “about how many reps” at a percentage, we find the whole number of reps whose average weight is closest. Our numbers sit close to the NSCA training load chart, which we show on the homepage for comparison.

How do you handle units and rounding?

• 1 kg = 2.20462262185 lb.
• Training weights are rounded to the nearest loadable step. The default is 5 lb or 2.5 kg. You can choose 2.5 lb, 1.25 kg, 1 kg, 0.5 kg, 1 lb, 10 lb or 5 kg.
• The headline 1RM is shown to one decimal place and is not rounded to plates, so you can see the raw estimate.

How does the plate calculator decide the plates?

We subtract the bar weight and split the rest in half for each side. We first load the biggest plates that fit, the way most lifters do. If that does not reach the target exactly, we search every combination of the plates you have. If the weight still cannot be made exactly, we show the nearest weights you can load below and above it. Default plates are 45, 35, 25, 10, 5 and 2.5 lb, or 25, 20, 15, 10, 5, 2.5 and 1.25 kg.

How is the warm-up ramp built?

The default ramp is an empty bar for 8 to 10 reps, then about 40% × 5, 60% × 3, 75% × 2, 85% × 1 and 92% × 1 of your top set. Each set is rounded to your plate step, never goes below the bar, and duplicates are removed. This is a common starting pattern, not a rule.

Where do the Wilks, DOTS and IPF GL numbers come from?

We use the published coefficients as implemented by the OpenPowerlifting project. Bodyweight and total are in kilograms (we convert from pounds for you).

• Wilks (1998): total × 500 / (a + b·x + c·x² + d·x³ + e·x⁴ + f·x⁵). Men: a = −216.0475144, b = 16.2606339, c = −0.002388645, d = −0.00113732, e = 7.01863E−06, f = −1.291E−08, bodyweight limited to 40–201.9 kg. Women: a = 594.31747775582, b = −27.23842536447, c = 0.82112226871, d = −0.00930733913, e = 0.00004731582, f = −0.00000009054, bodyweight limited to 26.51–154.53 kg.
• Wilks 2020: total × 600 / (same fifth-order form). Men: 47.4617885411949, 8.47206137941125, 0.073694103462609, −0.00139583381094385, 0.00000707665973070743, −0.0000000120804336482315 (40–200.95 kg). Women: −125.425539779509, 13.7121941940668, −0.0330725063103405, −0.0010504000506583, 0.00000938773881462799, −0.000000023334613884954 (40–150.95 kg).
• DOTS: total × 500 / (a + b·x + c·x² + d·x³ + e·x⁴). Men: −307.75076, 24.0900756, −0.1918759221, 0.0007391293, −0.0000010930 (40–210 kg). Women: −57.96288, 13.6175032, −0.1126655495, 0.0005158568, −0.0000010706 (40–150 kg).
• IPF GL points: total × 100 / (A − B × e^{−C × bodyweight}). Classic (raw) powerlifting: men A = 1199.72839, B = 1025.18162, C = 0.00921; women 610.32796, 1045.59282, 0.03048. Equipped powerlifting: men 1236.25115, 1449.21864, 0.01644; women 758.63878, 949.31382, 0.02435. Classic bench: men 320.98041, 281.40258, 0.01008; women 142.40398, 442.52671, 0.04724. Equipped bench: men 381.22073, 733.79378, 0.02398; women 221.82209, 357.00377, 0.02937.

How is the 5/3/1 cycle built?

The 5/3/1 program was created by Jim Wendler. Our tool takes a training max of 85% or 90% of your 1RM, then uses the widely published week percentages: 65/75/85% (week 1), 70/80/90% (week 2), 75/85/95% (week 3) and 40/50/60% for a deload week. For the full program, read Wendler’s book.

What can’t the calculators do?

• They cannot know your technique, depth, fatigue or experience. Real maxes can be higher or lower than the estimate.
• Research has found common 1RM equations underestimate the deadlift (LeSuer and colleagues, 1997).
• Estimates from more than 10 reps are much less reliable.
• Fast lifts such as the power clean are poorly suited to rep-based formulas. Use sets of 1 to 3.
• Nothing here is medical or coaching advice. See our disclaimer.

How do you test the calculators?

Every release runs an automated test suite before it goes live. It checks each formula against hand-worked examples (100 × 5 and 225 × 8), confirms that 1 rep returns the weight itself, checks RPE conversion, unit conversion, rounding, plate loading (including weights that cannot be made exactly), warm-ups, and the Wilks, Wilks 2020, IPF GL and DOTS results against published examples.

Found a mistake? Please tell us. We fix confirmed errors quickly and note them below.

Change log

• 30 September 2026: Site launched. 1RM engine with seven formulas, RPE, rep maxes, percentage tables, plate maths, warm-ups, Wilks (1998 and 2020), DOTS, IPF GL and 5/3/1. 83 automated checks passing.

Sources

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2. Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88-90.
3. Lander J. Maximum based on reps. National Strength and Conditioning Association Journal. 1985;6(6):60-61.
4. Lombardi VP. Beginning Weight Training. Dubuque, IA: W.C. Brown; 1989.
5. Mayhew JL, Ball TE, Arnold MD, Bowen JC. Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research. 1992;6(4):200-206.
6. O’Conner B, Simmons J, O’Shea P. Weight Training Today. St. Paul, MN: West Publishing; 1989.
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8. LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research. 1997;11(4):211-213. Abstract
9. Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research. 2006;20(3):584-592. PubMed 16937972
10. Zourdos MC, Klemp A, Dolan C, et al. Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. Journal of Strength and Conditioning Research. 2016;30(1):267-275. PubMed 26049792
11. Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength and Conditioning Journal. 2016;38(4):42-49. PubMed 27531969
12. National Strength and Conditioning Association. Training Load Chart. NSCA (PDF)
13. The OpenPowerlifting Project. Coefficient implementations for Wilks, Wilks 2020, Dots and IPF GL points (crates/coefficients). Source code
14. Wendler J. 5/3/1: The Simplest and Most Effective Training System for Raw Strength. 2nd ed. Jim Wendler LLC; 2011.