One Rep Max (1RM) Calculator

Estimated 1RM

{{ workingSetDisplay }} {{ strategyLabel }} TM {{ trainingMaxDisplay }} {{ spreadBadgeDisplay }} {{ confidenceLabel }}

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Working weight:

Example: 100 kg or 225 lb from one clean set of the same lift.

Reps completed:

Enter whole reps from the same set. Best range: 1-10; 11+ is planning-only.

Summary strategy:

Average is balanced; median ignores outliers; floor is conservative; ceiling is aggressive.

Training max:

Set 80-100%; use 85-90% for high-rep sets or wide formula spread.

{{ training_max_percent }}%

Plate preset:

Exact keeps decimals; kg/lb presets fill the rounding increment and mode.

Rounding:

Enter 0 for exact output, or set a plate jump such as 2.5 kg or 5 lb.

Load table range:

Choose start, end, and step percentages for the planning table.

Start:

Example: 50 for lighter entries.

End:

Use 100 to include the selected 1RM.

Step:

Example: 5 creates 50, 55, 60...

Included formulas:

Start with all seven, then remove a formula only for a coaching or comparison reason.

Formula	Est. 1RM ({{ unit }})	Delta vs selected	Copy
{{ row.label }}	{{ row.valueDisplay }}	{{ row.deltaDisplay }}

Area	Value	Detail
Selected estimate	{{ primaryEstimateDisplay }}	{{ strategyLabel }} · {{ confidenceLabel }}
Formula span	{{ formulaBandDisplay }}	{{ spreadDetailText }}
Current set intensity	{{ currentIntensityDisplay }}	{{ currentSetGuide }}
Training anchors	{{ trainingMaxDisplay }}	Triple {{ heavyTripleDisplay }} · five {{ volumeFiveDisplay }}
{{ row.label }}	{{ row.loadDisplay }}	Warm-up ladder

% of 1RM	Load ({{ unit }})	Load @ TM	Typical reps	Use	Copy
{{ row.pct }}%	{{ row.loadDisplay }}	{{ row.tmLoadDisplay }}	{{ row.repGuide }}	{{ row.focus }}

Reps	Max load ({{ unit }})	% of 1RM	Typical use	Copy
{{ row.reps }}	{{ row.loadDisplay }}	{{ row.intensityDisplay }}	{{ row.note }}

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Most lifters need a loading number more often than they need a true max attempt. A one-repetition maximum, or 1RM, is the heaviest load a person can complete once with acceptable technique for one specific lift. It is not a whole-body strength score. A bench press 1RM, squat 1RM, deadlift 1RM, and machine press 1RM each describe a different movement under a different technique standard.

Percentage-based training turns that movement-specific number into working weights. A set at 70% of 1RM usually leaves more room for volume and speed, while a set near 90% feels like heavy practice even before it reaches a true max. Coaches and training logs use those percentages to plan warm-ups, main work, peaking blocks, retests, and conservative training maxes.

Direct max testing can be useful, but it is a demanding measurement. Heavy singles need a good warm-up, reliable technique, enough rest between attempts, suitable equipment, and appropriate spotting or safeties. Fatigue, pain, unfamiliar equipment, or a rushed attempt can make the result less useful and more risky. Estimating 1RM from a completed set gives a planning anchor when a real max test is unnecessary or poorly timed.

A working set feeds a rep estimate, estimated 1RM, and training loads

Estimated 1RM equations work backward from a submaximal set. If 100 kg for 5 reps is close to the lifter's honest limit for that lift, the equations infer a likely single-rep load above 100 kg. The estimate becomes less stable when the set is far from failure, when the rep count is high, or when the lift is shaped strongly by technique, grip, tempo, range of motion, or endurance.

A useful estimate is therefore a planning anchor, not permission to attempt the number immediately. The same estimate can help choose working weights, compare progress across weeks, select a conservative training max, or spot a set that was too light or too heavy for its intended purpose.

Tested 1RM: The actual heaviest successful single under the day's conditions.
Estimated 1RM: A calculated projection from a completed set of weight and reps.
Training max: A buffered number below the estimate, often used to make day-to-day programming less brittle.

How to Use This Tool:

Enter one completed set, then review formula agreement and confidence before using the selected estimate for training loads.

Enter Working weight and choose kg or lb. Use the full load actually lifted, including the bar or machine setting when it applies.
Enter Reps completed as a whole number from the same set. A single rep returns the entered weight; sets above 10 show caution, and sets above 15 are labeled planning-only.
Open Advanced when you want to change Summary strategy. Consensus average is the default, while median, conservative floor, and aggressive ceiling change how the active formulas become the selected estimate.
Set Training max when you want a programming buffer below the selected estimate. The default 90% setting is useful when the source set is hard but not a direct max test.
Choose a Plate preset or custom Rounding. Exact output preserves decimals; kg and lb presets snap tables to common plate jumps such as 2.5 kg or 5 lb.
Set the load table with Start, End, and Step. If Start is above End, or Step is not greater than zero, the warning box explains what to fix.
Keep all Included formulas selected for a first pass, then compare Formula Consensus, Programming Brief, Training Loads, Rep Max Ladder, Formula Spread, Rep Intensity Map, and JSON before making a loading decision.

Interpreting Results:

Estimated 1RM is the selected summary of the active equations after the current rounding rule is applied. Read it with Formula span, Current set intensity, and the confidence badge. A tight span from a low-rep set is a stronger planning anchor than a wide span from a high-rep set.

High confidence means the source set used no more than 5 reps and the low-to-high formula spread is no more than 4% of the selected estimate. Moderate confidence allows up to 8 reps and up to 8% spread. Wider or higher-rep cases show Caution, which means the result is better for planning than for claiming a true max.

One rep max output interpretation cues
Output	How to read it	What to verify
`Formula Consensus`	Each active equation's estimate and delta from the selected result.	Large positive and negative deltas mean the set is a weaker anchor.
`Programming Brief`	Selected estimate, formula span, current set intensity, training anchors, and warm-up ladder.	Check whether the current set intensity matches how the set actually felt.
`Training Loads`	Percentage rows applied to both selected 1RM and training max.	Confirm rounding and range settings before putting the numbers into a program.
`Rep Max Ladder`	Estimated max loads for 1 to 12 reps using the same formula choices and strategy.	Use it as a planning guide, not a guarantee that every listed rep target is available today.
`Rep Intensity Map`	A chart view of rep targets, current set intensity, and the training max marker.	Look for mismatches between the visual intensity zone and the session goal.

A high estimate does not cancel ordinary lifting judgment. Keep technique, spotting, safeties, fatigue, injury history, and lift familiarity ahead of the number when deciding whether to test a heavy single.

Technical Details:

Submaximal 1RM prediction assumes that a heavier single and a lighter multi-rep set are connected by a repeatable fatigue relationship. The relationship is useful, but it is not identical for every lift or every lifter. Large compound lifts, machine exercises, isolation movements, bodyweight variations, and endurance-biased athletes can all produce different rep-to-percentage patterns.

Seven equations are evaluated from the same working weight and completed reps. Linear equations such as Epley and O'Conner add a fixed percentage per rep. Curved equations such as Mayhew and Wathan change more gradually as reps rise. Comparing several equations is useful because one formula can look precise while hiding the uncertainty that appears when formulas disagree.

Formula Core

\begin{array}{rcl} E_{i} & = & f_{i} (w, r) \\ selected 1RM & = & mean, median, minimum, or maximum of active estimates \\ training max & = & selected 1RM \times \frac{training max percent}{100} \\ current set intensity & = & \frac{w}{selected 1RM} \times 100 \end{array}

Here w is working weight and r is completed reps. If r = 1, every active formula returns the entered working weight. For higher reps, the active equations produce candidate estimates before the selected summary strategy and rounding rule are applied.

One rep max equations used by the calculator
Formula	Estimate from weight w and reps r
Epley	`w x (1 + r / 30)`
Brzycki	`w x 36 / (37 - r)`
Lombardi	`w x r^0.10`
Mayhew	`100 x w / (52.2 + 41.9 x e^(-0.055 x r))`
O'Conner	`w x (1 + 0.025 x r)`
Wathan	`100 x w / (48.8 + 53.8 x e^(-0.075 x r))`
Lander	`100 x w / (101.3 - 2.67123 x r)`

For a 100 kg set of 5 reps, Epley gives 100 x (1 + 5 / 30) = 116.67 kg. With all seven formulas active and the consensus average strategy, the selected estimate is about 115.49 kg before rounding. A 90% training max from that selected estimate is about 103.94 kg before plate rounding.

Confidence thresholds for one rep max estimates
Confidence label	Rep condition	Formula spread condition	Practical reading
High confidence	`reps <= 5`	`spread <= 4%`	Strong planning estimate when the set was technically clean and near enough to failure.
Moderate confidence	`reps <= 8`	`spread <= 8%`	Useful for programming, with room for conservative load choices.
Caution	Anything higher	Anything wider	Better for broad planning than for claiming or testing a max.

Training load intensity guide
Percent of 1RM	Label	Typical reps	Use cue
0-<60%	Technique / speed	6-10	Keep bar speed high.
60-<70%	Volume	5-8	Stable workload for repeated sets.
70-<80%	Base strength	3-6	Useful main-work range for many lifts.
80-<87%	Heavy strength	2-4	Lower-fatigue heavy work.
87-<94%	Peak practice	1-3	Singles and doubles near the top end.
94-100%	Max test	1	Treat as testing, not volume work.

The rep ladder reverses the active formulas against the selected estimate for 1 to 12 reps, then applies the same summary strategy and rounding. Plate rounding changes displayed load choices, but it does not change the raw formula comparison or the underlying formula spread.

Accuracy Notes:

Estimated 1RM is informational training guidance, not medical advice, injury clearance, or proof that a heavy single is safe today. It is most useful when the source set uses the same lift, equipment, range of motion, and technique standard that you want to plan from.

Sets above about 10 reps need extra caution because equations have more room to diverge.
Sets above 15 reps are planning-only estimates and can drift badly from a true tested max.
A set stopped with several reps in reserve can understate strength or make different formulas appear falsely precise.
A set performed with unusual tempo, shortened range of motion, straps, bounce, or different equipment should not be compared as if it were the same test.
Use spotters, safeties, conservative jumps, and professional coaching or medical guidance when a heavy attempt carries extra risk.

Worked Examples:

Heavy triple for a main lift. A lifter enters 140 kg for 3 reps with all seven formulas active and exact rounding. The consensus average is about 153.03 kg, with a formula span of roughly 148.24-159.59 kg. The Programming Brief shows the current set around 91.5% of 1RM, so the set is a strong anchor, but the top of the span should not be treated as automatic.

Higher-rep planning set. A set of 80 kg for 12 reps can still build useful percentage rows, but the formulas spread from about 102.57 kg to 115.53 kg. The confidence label moves to Caution, so the Training max and rounded Training Loads are safer planning references than a direct max attempt.

Plate rounding changes the usable prescription. A 225 lb set for 5 reps averages about 259.85 lb before rounding, with a 90% training max near 233.87 lb. Choosing 5 lb gym jumps changes the displayed rows to loadable numbers while the formula spread remains based on the raw estimates.

Range correction. If Start is set above End, the warning box says the load table range must start at or below the end percent. Lower Start or raise End, then recheck Training Loads and Rep Intensity Map before copying or downloading the result.

FAQ:

Which 1RM formula should I trust?

Start by keeping all seven formulas selected and read Formula span. If the spread is tight, the exact formula matters less. If the spread is wide, use the median or conservative floor and treat the estimate as planning guidance.

Why does the same set produce several max numbers?

Each equation models rep fatigue differently. Formula Consensus shows those differences instead of hiding them behind one number.

Should I program from Estimated 1RM or Training max?

Use Estimated 1RM to understand the likely max anchor. Use Training max for routine working weights when fatigue, high reps, technique variation, or a wide formula spread make the estimate less certain.

Does plate rounding change the formula result?

No. Plate preset, Rounding increment, and Rounding mode change displayed loads and table rows, while Formula span still comes from the raw active equations.

Can I compare estimates across weeks?

Yes, but keep the lift, equipment, range of motion, rep target, and summary strategy consistent. A clean 5-rep set compared with another clean 5-rep set is usually more meaningful than comparing a grinder triple with a rushed 12-rep set.

Why did I get warnings or an empty table?

Check that Working weight is positive, Reps completed is at least 1, at least one formula is selected, Start is not above End, and Step is greater than zero.

Glossary:

1RM: The heaviest successful single for a specific lift under a specific technique standard.
Working set: The completed set whose weight and reps become the estimate input.
Formula span: The low-to-high range across the active 1RM equations.
Training max: A buffered value below the selected estimate, used to make percentage loading more conservative.
Current set intensity: The entered working weight expressed as a percentage of the selected 1RM.
Plate preset: A rounding setup that snaps calculated loads to common kg or lb increments.

References:

What is a one-rep max?, Human Performance Resources by CHAMP, July 5, 2022.
Using Intensity Based on Sets and Repetitions, National Strength and Conditioning Association.
NSCA Training Load Chart, National Strength and Conditioning Association.
The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift, Journal of Strength and Conditioning Research, November 1997.
Developing Accurate Repetition Prediction Equations for Trained Older Adults with Osteopenia, PMC.