One-Rep Max (1RM) Calculator

About this calculator

Estimate your one-rep max from a submaximal set, explore 60–100% training weights, and work out a practical barbell load with clear assumptions.

Rep-based equations provide estimated 1RM values. They do not directly measure maximal strength, and accuracy varies across exercises, rep ranges and individuals.

How to use the One-Rep Max Calculator

Enter the weight lifted, completed repetitions and exercise. For a barbell lift, include the bar in the weight. Use a consistent convention for other equipment. Confirm adult use and select Calculate 1RM. Valid edits then update the results.

The example is 100 kg for six Bench Press repetitions. Unit switching converts the lift without clearing it. Exercise is context only: Bench Press, Squat, Deadlift, Overhead Press and Other all use the same equations. An equipment display does not make these equations equally accurate for every movement.

What one-rep max means

A one-repetition maximum is the largest load someone can lift once under the conditions of a particular exercise and technique. This page estimates that value from a recorded set; it does not observe the lift or establish a safe maximum.

Range of motion, pauses, equipment, fatigue and technique affect comparisons. Use like-for-like sets when interpreting estimates over time.

Why estimate instead of testing directly

A submaximal set can provide a useful reference without requiring a maximal attempt. Do not test a true maximum just to use this page.

ACSM’s historical 2009 progression guidance described 8–12RM loads for novices, rather than making maximal testing a prerequisite. The 2026 ACSM synthesis updates that guidance. Neither source turns a calculator prediction into an instruction to lift the displayed maximum.

The Epley formula

Epley: estimated 1RM = weight × (1 + reps / 30).

This is the headline method because it is simple and predictable, not because it is universally the most accurate. For one completed rep with RIR off, the tool returns the lifted weight directly instead of inflating it. Epley is never averaged with the comparison equations.

The exact implementation uses 1/30. Some research tables print its coefficient as 0.033; that rounded coefficient produces a slightly different result. The formula above defines this calculator’s arithmetic.

The Brzycki formula

Brzycki: estimated 1RM = weight × 36 / (37 − reps).

This rational form is used consistently here. Research tables also present the rounded-coefficient form weight / (1.0278 − 0.0278 × reps); the tiny coefficient difference is not additional knowledge about your strength. The shared one-rep direct-return rule applies.

The Lombardi formula

Lombardi: estimated 1RM = weight × reps^0.10.

This nonlinear equation appears alongside Epley and Brzycki in the prediction-equation literature, including Whisenant and colleagues’ comparison table. It also returns the lifted weight at one rep. The expandable comparison uses one decimal to show equation differences without implying that precision is achievable.

Why equations give different answers

Equations encode different mathematical relationships between repetitions and load. Whisenant and colleagues compared prediction equations using collegiate football players’ bench-press data; performance depended on repetition count. Reynolds and colleagues examined multiple-repetition testing in bench and leg press, illustrating why a result depends on the test and exercise context.

A strong group correlation does not guarantee a close estimate for an individual. Training status and population matter. Exercise-specific formula switching is deliberately absent in this version; there is no claim that one equation wins for every lift.

Rep range and estimation accuracy

The supported completed-rep range is 1–12. This is a product boundary informed by reduced usefulness of high-rep prediction, not a biological cutoff. A caution appears above ten completed or effective reps. It does not say every twelve-rep estimate is wrong.

The equations are most meaningful when the entered set reflects proximity to a repetition limit. A comfortably stopped set may underestimate capacity, but the tool does not ask you to force failure or attempt a maximal lift to improve a number.

How 1RM percentages are used

A percentage is simply estimated 1RM multiplied by that fraction. An 80% target from 120 kg is 96 kg before display rounding.

The 2026 ACSM overview reports that heavier loading, including at least 80% 1RM, can enhance voluntary strength in healthy adults. Adaptations also depend on exercise selection, volume and other factors. This is educational context, not a session prescription or a claim that everyone should use heavy loads.

Using the training-weight table

The table runs from 100% to 60% in five-point steps. Typical-use labels describe relative loading only; no guaranteed repetition ranges are provided. Your possible repetitions vary by exercise and individual.

Custom percentage accepts 40–100%, initially 87.5%. It changes only that derived target and a plate helper explicitly set to Custom percentage. It never changes the headline, source set or main table.

Display rounds to the nearest 0.5 kg or 1 lb. Tiny positive amounts that would round to zero are labeled below the display increment. Internal precision is retained for percentages, plate loading and saved estimates. Units use 1 kg = 2.20462262185 lb; repeated switches retain canonical kilograms.

How plate loading works

Open Show plates, choose a table percentage or the custom target, then choose the bar and enabled plate sizes. A plate value means one plate on each side. Total load = bar + 2 × sum of one side’s plates.

Metric presets are 20/15 kg bars and 25, 20, 15, 10, 5, 2.5, 1.25, 0.5 kg plates. US presets are 45/35 lb bars and 45, 35, 25, 10, 5, 2.5 lb plates. Custom bars accept 1–250 in the chosen unit with two decimals. Unit switching preserves the lift but resets these equipment presets; a 45 lb bar is not treated as exactly 20 kg.

The helper searches achievable paired loads with up to twelve plates per side, assuming enough matching pairs of every enabled size. It chooses minimum absolute difference, then the lower load on a tie, then fewer plates. It can find solutions a largest-plate-first shortcut would miss. Available sleeve space, inventory and equipment ratings must still be checked.

Exact and closest loads remain separate from the mathematical target, with a signed difference. A below-bar target asks for a lighter bar and produces no negative plates. Empty inventory means bar only. A closest load above the target is explicitly identified, not silently substituted or recommended. Collars are not added automatically; account for them in custom bar weight if needed.

What reps in reserve means

Reps in reserve (RIR) is your estimate of how many more repetitions you could have completed. The optional advanced mode adds 1–4 RIR to completed reps, then feeds that effective count into each equation. It labels the result RIR-adjusted estimate.

This is a product approximation, not a directly measured failure set. Research on predicting remaining repetitions shows imperfect accuracy. Six completed reps plus four imagined reps do not carry the same certainty as a completed ten-rep set.

Effective reps must stay at or below twelve; otherwise results are suppressed until the adjustment is reduced or disabled. For one completed rep, turn RIR off: this version preserves the direct-return rule instead of inflating a one-rep entry through advanced mode.

Optional local history and privacy

Nothing is saved automatically. Save result locally keeps up to ten estimates in this browser, storing exercise, full-precision estimated 1RM, display unit, Epley/RIR method and save time. It omits source weight, reps and RIR values. These derived results can still be sensitive.

Show saved lifts reads that history only when chosen. Refresh saved lifts reloads it; Delete and Clear saved lifts remove records. The calculator itself resets after a page refresh. History is not an account, synced backup or guarantee against browser storage being cleared.

Estimated change compares the latest two saves for the same exercise and method in canonical kilograms. Differences may reflect prediction noise, technique or conditions, not proven strength gains. Saving works after Reject all and is separate from analytics/advertising choices. Copy/share is also explicit and includes the source set, as disclosed beside those buttons; it creates no input-containing URL.

Estimation limitations

Adult educational use only. The supported weight range is 0.1–1,000 kg or the lb equivalent as an engineering limit, not a classification of realistic or safe lifts. The formula does not inspect technique or infer body weight, age, sex, training experience or injury status.

The three estimates and table cannot replace coaching, individualized medical restrictions or equipment checks. Percentage labels do not specify sets, repetitions, rest periods, frequency or a progression plan. Formula disagreement is not a personalized confidence interval.

Safety and technique

Use loads you can control with good technique, suitable equipment and appropriate supervision or spotting. Stop for pain or concerning symptoms. A listed load, adult checkbox or exact plate combination is not clearance to attempt it.

NSCA’s safety discussion emphasizes appropriate technique and controlled progression without requiring extreme loading. This calculator does not prescribe a true maximum, diagnose injury or provide youth, pregnancy, rehabilitation or therapeutic exercise targets. Follow individualized professional guidance when those circumstances apply.

Worked example

Bench Press, 100 kg × six completed reps, RIR off:

• Epley: 120.0 kg.
• Brzycki: 116.1 kg.
• Lombardi: 119.6 kg.

Training targets from the headline:

• 100% → 120 kg
• 95% → 114 kg
• 90% → 108 kg
• 85% → 102 kg
• 80% → 96 kg
• 75% → 90 kg
• 70% → 84 kg
• 65% → 78 kg
• 60% → 72 kg

Custom 87.5% → 105 kg. At 80%, the unrounded target is 96 kg. With the 20 kg bar and default plate options, one side is 25 + 10 + 2.5 + 0.5 kg, giving 96 kg total. Different inventories can produce a different closest load.

One-rep max FAQ

What is a one-rep max?

The maximum load lifted once for a particular exercise under particular conditions. This page estimates it; it does not measure it.

How is estimated 1RM calculated?

The headline uses Epley: weight × (1 + reps/30), with lifted weight returned directly for one rep.

Is Epley accurate?

It can be useful, but individual error varies. No equation is guaranteed best across all exercises, rep ranges and people.

Why do formulas give different results?

They model the repetitions/load relationship differently. The comparison illustrates variation and is not averaged into the headline.

How many reps should I enter?

Use a completed set within 1–12 reps. Above ten, the tool cautions that precision usually decreases. Do not force failure to use it.

Do I need to test a true maximum?

No. A submaximal set is sufficient for an estimate. The result does not instruct you to attempt the predicted maximum.

What does 80% of 1RM mean?

It is 0.8 times the estimate. Possible repetitions and suitable training uses depend on the individual and exercise.

How does the plate calculator work?

It searches paired plate combinations and shows the closest achievable total, with lower load winning equal-distance ties. Check real inventory and equipment capacity.

What does RIR mean?

Reps in reserve estimates repetitions left. Advanced mode adds that guess to completed reps within the supported range; it remains an approximation.

Does BuzCalculator save my lifting data?

Only when you select Save result locally. You can view, delete or clear up to ten saved estimates in this browser. No automatic lift history, account or cloud sync is used.

Sources and methodology review

Methodology reviewed September 28, 2026. Research supports equation provenance and limitations, not universal accuracy or this product’s RIR method, plate inventory, review bounds or typical-use labels. The 2009 ACSM source is historical context; the 2026 synthesis is the current context reviewed here.

• Whisenant et al. (2003): Validation of submaximal 1RM prediction equations (opens in a new tab)
• Whisenant et al.: Full paper and equation table (research-paper copy) (opens in a new tab)
• Reynolds et al. (2006): Prediction from multiple repetition maximum testing (opens in a new tab)
• ACSM (2026): Resistance training prescription — overview of reviews (opens in a new tab)
• ACSM (2009): Progression models in resistance training — historical novice context (opens in a new tab)
• NSCA (2026): Resistance-training safety and controlled progression (opens in a new tab)
• Halperin et al. (2022): Accuracy in predicting repetitions to task failure (opens in a new tab)