The science behind the numbers

WeightIQ does a small amount of maths for you. This page lists every calculation, what published research says about it, and where it is weak. The honest summary: these are estimates and common conventions, not measurements and not a prescription. They are useful for planning and for seeing trends, and they can be wrong for you. Please read the safety notice too.

On this page: Estimated and potential 1RM · Percentages and zones · Next-session suggestion · Warm-up ramps · Progress projection · Goals · Plates and units · Safety facts · Sources

Estimated and potential 1RM

What WeightIQ does. For each set it estimates your one-rep max (1RM) with the Epley formula: weight × (1 + reps ÷ 30). A set of 245 lb × 5 gives 285.8 lb. A single rep counts as is. Your potential 1RM for an exercise is the highest estimate among your completed sets of 10 reps or fewer; sets above 10 reps are left out, and the 1RM calculator warns about them too.

What research says. The formula comes from a 1985 strength-coaching booklet [1]; the other well-known equation is Brzycki's [2]. A 1997 comparison of several equations (Epley's among them) found their predictions tracked real 1RMs closely, but how accurate they were in pounds depended on the lift, and they under-estimated the deadlift [3]. A 2024 meta-regression pooled 952 repetitions-to-failure tests from 7,289 people in 269 studies and measured how many reps people can really do at each percentage of their 1RM [4]. On average people managed about 5 reps at 90% and about 15 at 70%, but people differ a lot (one standard deviation is about 2.5 reps at 80% and about 4.4 reps at 60%), and the leg press allows many more reps than the bench press at the same percentage.

Our check of Epley against those averages. If you do r reps with a weight that really is p of your 1RM, Epley's estimate divided by your true 1RM is (1 + r ÷ 30) × p. Using the average reps reported in [4]:

These rows are our own arithmetic from published average values, not results reported in the paper. The averages for most other exercises are read from the paper's discussion and are approximate. Individual people vary around them: one standard deviation of 2.5 reps at 80% moves Epley's estimate by roughly 7% of your 1RM.

Where it falls short. Epley tends to read a little high, much higher for machine-like leg movements, and it is least reliable for sets of many reps, where fatigue resistance matters more than strength. Taking the highest of several noisy estimates also leans high by construction. So treat estimated and potential 1RM as a guide that can be several percent above what you could actually lift on a good day. We keep Epley because it is simple, widely used and consistent, and we label the result as an estimate. For that reason the potential 1RM, the weekly best estimate on the progress charts and goal progress ignore sets of more than 10 reps, where the estimate is least trustworthy.

Percentages and training zones

What WeightIQ does. The 1RM calculator shows a table from 100% down in 5% steps, rounded to weights you can load (5 lb or 2.5 kg steps). The progress chart draws reference lines at 75%, 85% and 95% of your current or projected estimated 1RM.

What research says. The 2026 American College of Sports Medicine (ACSM) position stand found heavier loads (80% of 1RM and above) went with larger strength gains, while muscle growth was similar across loads from 30% to 100% of 1RM [6]. The same research also shows that the reps you can do at a percentage vary by exercise and by person [4]. In one small study, endurance runners did about 40 leg-press reps at 70% of their 1RM where weightlifters did about 18 [5].

Where it falls short. A percentage is a reference point, not a rule: two people at 75% can face very different sets. Use the zones to see where a weight sits, and choose weights you can lift safely.

Next-session suggestion

What WeightIQ does. After a strength exercise, if every set at your top weight reached its planned reps, it suggests adding one plate step (5 lb, or 2.5 kg) next time. If a set was skipped or short, it suggests repeating the weight.

What research says. Progressively increasing the challenge matters for long-term gains, but the current ACSM position stand names no specific amount: it says load can go up by changing the percentage of 1RM, retesting, or using effort ratings, and that there is not enough evidence to set exact effort targets [6]. The older 2009 stand suggested a 2–10% increase once you could do one or two reps over the target [7]. Effort scales that ask how many reps you had left (reps in reserve) have been proposed and studied [8]; WeightIQ does not ask for an effort rating yet.

Where it falls short. A flat 5 lb step is a small change on a heavy lift and a big one on a light lift: about 2% on a 245 lb squat, 4% on 135 lb, 5% on 95 lb, and 11% on a 45 lb bar (our arithmetic). It is a conservative convention for heavy lifts, not a research-derived rule. Take smaller steps (fractional plates) when 5 lb is too much.

Warm-up ramps

What WeightIQ does. The Suggest sets tool builds a ladder of lighter sets up to your top set, in four styles (Standard, Low fatigue, Powerlifting, Even steps). The default Standard style uses about 46%, 62%, 78% and 90% of the top weight.

What research says. Small trials in trained men found that warming up with progressively heavier sets helped the first working sets more than a single light set: in a 40-man study, a single set at 40% of the working load did worst, a single heavy set suited the squat, and two progressive sets suited the bench press, although several differences were small or not statistically significant [9]. A 2021 systematic review of 11 studies concluded that a specific warm-up at loads close to the maximum can improve maximal strength and reps [10].

Where it falls short. No study validates a particular ladder: the exact percentages are a coaching convention. Heavy warm-up sets should use few reps so they do not tire you; WeightIQ keeps the planned reps the same on every ramp set today, so lower the reps yourself on the heavy ramp sets. Every style is a starting point, never a prescription.

Progress charts and projection

What WeightIQ does. The Progress chart plots your best estimated 1RM per week. With at least 6 sessions over 4 weeks it can draw a projection for the next 4, 12 or 26 weeks, with 75%, 85% and 95% likelihood bands. The curve is a saturating curve (gains slow down) fitted to your own history, with a plateau check and hard ceilings of +3% (4 weeks), +7% (12 weeks) and +12% (26 weeks) over your current estimate.

What research says. There is no published curve that forecasts one person's lift. Average gains differ by training experience and by body region: for example, a meta-analysis in women found trained women gained lower-body strength faster than upper-body strength, with no such difference in beginners [11]. Individual response varies widely.

Where it falls short. The shape (diminishing returns) and the personal fit are modelling choices; the +3 / +7 / +12% ceilings are our own conservative limits, not figures from a study. The projection cannot see illness, a deload, an injury or a change of programme. It is an estimate with a band, not a promise, and the app says so on screen.

Goals

What WeightIQ does. A goal is a target for one exercise (a 1RM, a weight for reps, reps, a hold or a time). Progress is (now − start) ÷ (target − start). For 1RM goals “now” is your potential 1RM, so a heavier-rep set can reach the goal through the estimate (the app tells you when it did). For times, lower is better. A goal counts as reached the first time a set meets it.

What research says. Goal-setting research finds that specific, challenging goals tend to lead to better performance than vague ones [12], and a meta-analysis found that setting goals can change behaviour [13]. Effects vary between people and settings.

Where it falls short. A goal on a number is not a reason to rush, skip warm-ups, cut range of motion or train through pain. Set goals you can reach safely, and change them freely.

Plates and units

What WeightIQ does. It shows the plates for each side: (total − bar) ÷ 2, using the plates you have. It converts between pounds and kilograms (1 lb = 0.4536 kg; the factor is 0.4535924 in [14]) and uses the standard 45 lb (20 kg) and 35 lb (15 kg) bars.

Evidence. This is arithmetic, not research. Real plates and bars can differ slightly from their labels, so the total on the bar can be off by a small amount.

Safety facts

• The 2026 ACSM position stand concludes that resistance training is safe for healthy adults of all ages, and that training to failure is not necessary for gains; it mentions aiming to finish sets with about 2–3 reps in reserve [6].
• A systematic review of the weight-training sports found injury rates that are low compared with common team sports (for example about 0.24–1 injury per 1,000 hours in bodybuilding and about 4.5–6.1 in strongman), but the studies were mostly of limited quality [15].
• ACSM's health-screening guidance bases its advice on how active you are now, whether you have symptoms or known heart, metabolic or kidney disease, and how hard you plan to train: if you are not active yet and have symptoms or a known condition, talk to a doctor before starting [16].

None of this makes WeightIQ medical advice or a replacement for a qualified coach. Read the safety notice.

What we do not claim

• That any number here is your true 1RM, a safe weight, or a prediction you can rely on.
• That the warm-up ladders, the +5 lb step or the 75/85/95% zones are optimal for you.
• That WeightIQ can replace a doctor, physiotherapist or coach.

Found a mistake or a better source? Email [email protected] and we will check and correct it.

Sources

1. Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985. (A booklet; no online copy.)
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. doi:10.1080/07303084.1993.10606684
3. 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.
4. Nuzzo JL, Pinto MD, Nosaka K, Steele J. Maximal number of repetitions at percentages of the one repetition maximum: a meta-regression and moderator analysis of sex, age, training status, and exercise. Sports Medicine. 2024;54(2):303–321. doi:10.1007/s40279-023-01937-7 (open access)
5. Richens B, Cleather DJ. The relationship between the number of repetitions performed at given intensities is different in endurance and strength trained athletes. Biology of Sport. 2014;31(2):157–161. doi:10.5604/20831862.1099047
6. Currier BS, D'Souza AC, Fiatarone Singh MA, et al. American College of Sports Medicine position stand. Resistance training prescription for muscle function, hypertrophy, and physical performance in healthy adults: an overview of reviews. Medicine & Science in Sports & Exercise. 2026;58(4):851–872. doi:10.1249/MSS.0000000000003897
7. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Medicine & Science in Sports & Exercise. 2009;41(3):687–708. doi:10.1249/MSS.0b013e3181915670 (superseded by [6])
8. 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. doi:10.1519/JSC.0000000000001049
9. Ribeiro B, Pereira A, Neves PP, et al. The role of specific warm-up during bench press and squat exercises: a novel approach. International Journal of Environmental Research and Public Health. 2020;17(18):6882. doi:10.3390/ijerph17186882
10. Ribeiro B, et al. The effect of warm-up in resistance training and strength performance: a systematic review. Motricidade. 2021. Journal page
11. Jung R, Gehlert S, Geisler S, et al. Muscle strength gains per week are higher in the lower-body than the upper-body in resistance training experienced healthy young women: a systematic review with meta-analysis. PLOS ONE. 2023;18(4):e0284216. doi:10.1371/journal.pone.0284216
12. Locke EA, Latham GP. Building a practically useful theory of goal setting and task motivation: a 35-year odyssey. American Psychologist. 2002;57(9):705–717. doi:10.1037/0003-066X.57.9.705
13. Epton T, Currie S, Armitage CJ. Unique effects of setting goals on behavior change: systematic review and meta-analysis. Journal of Consulting and Clinical Psychology. 2017;85(12):1182–1198. doi:10.1037/ccp0000260
14. Thompson A, Taylor BN. Guide for the Use of the International System of Units (SI), NIST Special Publication 811, Appendix B (conversion factors). nist.gov
15. Keogh JWL, Winwood PW. The epidemiology of injuries across the weight-training sports. Sports Medicine. 2017;47(3):479–501. doi:10.1007/s40279-016-0575-0
16. Riebe D, Franklin BA, Thompson PD, et al. Updating ACSM's recommendations for exercise preparticipation health screening. Medicine & Science in Sports & Exercise. 2015;47(11):2473–2479. doi:10.1249/MSS.0000000000000664