| Formula | Est. 1RM ({{ unit }}) | Copy |
|---|---|---|
| {{ row.label }} | {{ row.valueDisplay }} |
| % of 1RM | Load ({{ unit }}) | Copy |
|---|---|---|
| {{ r.pct }}% | {{ r.loadDisplay }} | |
| No rows | ||
One repetition maximum describes the heaviest load you can control for a single rep while staying in the groove. Strength coaches rely on that snapshot to schedule training stress, progress volume, and compare lifts across sessions. Estimating it from submaximal sets lets you plan heavy work without risky daily max attempts.
You enter the heaviest clean set weight, record how many strict repetitions it took, choose the formulas you trust, and the calculator returns both an average anchor and the individual estimates. You can round the result to match plates, spin up the percent table that maps common training zones, and copy downloads for quick programming notes. Keeping every formula side by side shows how sensitive the answer is to endurance versus neural drive.
A lifter completing five tidy reps at 100 kilograms often sees the average settle near 115 kilograms while the spread across formulas stays within a few kilos. The percent table then lists ready made loads at 60 to 90 percent for warm ups, main sets, and back off work in the same unit you entered. Saving the JSON snapshot or CSV export preserves the exact assumptions so later comparisons stay honest.
Keep rep quality tight, stop one or two shy of failure, and log the same lift variation each time so comparisons stay fair. If fatigue builds or tempo drifts, rerun the test with lower repetitions or defer the estimate to protect recovery. Treat the low and high ends of the formula range as planning guard rails instead of proof that one number is exact.
Reach for this estimator when you want fast programming guidance across several accessories, and switch to velocity tracking or formal max testing blocks when you need lab grade diagnostics. Reset the page before handing a device to someone else if you do not want to share your recent training numbers.
The calculator models the relationship between working weight W, completed repetitions R, and the inferred one repetition maximum M. Each formula encodes a curve derived from cohort testing that ties muscular endurance to peak force for the target lifts. These estimates assume steady tempo, full range of motion, and no grinders.
Seven published regressions are available: Epley, Brzycki, Lombardi, Mayhew, O'Conner, Wathan, and Lander. Each uses a distinct blend of linear or exponential scaling to describe how quickly strength decays as repetitions increase. Calculating M across the enabled formulas and averaging the raw values produces a central guide while still surfacing the individual rows.
The percent table multiplies the unrounded mean by user selected percentages from the chosen start through the end step and then applies the rounding increment. Loads remain in the input unit so plate math stays simple for both metric and imperial gyms. Because the table draws from the averaged value, toggling formulas immediately shifts every downstream load.
Reliability peaks between one and twelve repetitions, and convergence is tightest between three and six reps. Above that span, endurance capacity inflates the estimate, especially for lifters with methodical grinding tempo. The interface raises warnings when an entry leaves the supported window so coaches can confirm with another test.
| Symbol | Meaning | Unit / datatype | Source |
|---|---|---|---|
| Working-set load entered by the lifter | kg or lb | Input | |
| Strict repetitions completed in the set | integer | Input | |
| Per-formula one rep max estimate | kg or lb | Derived | |
| Arithmetic mean of enabled formulas | kg or lb | Derived | |
| Percent used for training load table | percent | Input |
Enter 100 kilograms for W, five repetitions for R, keep every formula active, and round to the nearest 2.5 kilograms while building a percent table from 60 to 90 percent in five point steps.
The formulas cluster within about 6 kilograms, so the mean of 115.49 kilograms is reasonable for planning. The rounded table yields 70, 75, 80, 87.5, 92.5, 97.5, and 105 kilograms, giving immediate targets for warm up, main work, and back off sets without replying on ad hoc plate math.
| Formula | Best rep span | Typical drift |
|---|---|---|
| Epley | 1 to 12 | Leans high when R exceeds 10 because of the linear slope. |
| Brzycki | 1 to 10 | Slightly conservative above eight reps, useful for bench and squat. |
| Lombardi | 3 to 15 | Logarithmic curve keeps long sets from exploding, pairs well with bodybuilding work. |
| Mayhew | 1 to 10 | Derived from football bench testing, trends optimistic for lower body lifts. |
| O'Conner | 1 to 8 | Simple multiplier that mirrors early linear gains; loses precision on higher reps. |
| Wathan | 1 to 10 | Exponential model reacts quickly to fatigue; helpful for speed focused blocks. |
| Lander | 1 to 10 | Stable for field athletes; underestimates when R equals one because the denominator caps the curve. |
This utility offers informational estimates only and is not a substitute for supervised max testing, medical clearance, or individualized coaching.
Example: enter 225 pounds for six reps, round to the nearest five, and generate a 55 to 90 percent table in five point increments for a press cycle.
You finish with a ready list of target loads, a record of which formulas drove the average, and a shareable payload for teammates or clients.
| Parameter | Meaning | Unit / datatype | Typical range | Sensitivity |
|---|---|---|---|---|
| Weight lifted | Heaviest strict set used for the estimate | kg or lb | 40 to 350 | Direct impact on every formula |
| Reps performed | Completed repetitions without form breakdown | integer | 1 to 12 | Sets the slope of the regression curves |
| Rounding increment | Plate-compatible step applied to outputs | kg or lb | 0 to 10 | Alters displayed totals, not raw math |
| Percent range | Start, end, and step for load table | percent | 40 to 110 | Determines how many rows appear |
| Formula toggles | Enable or disable specific regressions | boolean | On / Off | Influences the average and displayed spread |
Internal calculations use IEEE 754 double precision with a period as the decimal separator. Displayed values default to two decimal places. When rounding is enabled, the tool divides by the increment, applies banker style nearest rounding (ties round to the nearest even integer), and multiplies back to produce plate friendly numbers. Percent table rows inherit the same increment so the JSON and CSV exports match the on-screen table.
| Field | Type | Accepted values | Notes | Placeholder |
|---|---|---|---|---|
| weight_value | number | > 0 | Step 0.1; warning if zero or negative. | 100 |
| unit | enum | kg, lb | Units propagate to tables and exports. | kg |
| reps | integer | ≥ 1 | Step 1; warnings above 12 reps. | 5 |
| round_increment | number | ≥ 0 | Step 0.1; zero disables rounding. | 2.5 |
| round_mode | enum | nearest, down, up | Applies to main value and percent table. | nearest |
| start_percent | integer | ≥ 1 | Must not exceed end_percent. | 60 |
| end_percent | integer | ≤ 200 | Must be ≥ start_percent. | 100 |
| step_percent | integer | ≥ 1 | Values outside 1 to 30 reset to defaults. | 5 |
| use_{formula} | boolean | true / false | At least one formula must stay enabled. | true |
| Query params | URL | Serialized values | Written after interaction for sharing. | N/A |
| Channel | Content | Encoding | Precision |
|---|---|---|---|
| UI summary | Average 1RM, formula count, rounding info | Float, 2 dp | Rounded per settings |
| Metrics CSV | Formula labels with raw and rounded values | UTF-8 CSV | 4 dp raw, 2 dp rounded |
| Percent CSV | Percent and load pairs | UTF-8 CSV | Matches rounding increment |
| JSON export | Inputs, per formula results, percent table | UTF-8 JSON | Full precision |
| Query string | weight_value, reps, percent bounds, toggles | URL encoded | Exact values |
All calculations, charts, CSV downloads, and JSON exports execute entirely in the browser; no external APIs, analytics beacons, or background requests are invoked.
State lives in reactive memory and, after interaction, in the optional query string. Reloading without the encoded parameters clears the session immediately.
The computation pipeline touches a constant number of formulas, so time complexity is O(1) relative to the input size, and the percent table loops over at most 200 rows. Memory usage is bounded by the two result arrays, keeping the tool responsive even on low-power devices.
Identical inputs always yield the same per-formula values, arithmetic mean, warnings, charts, and exports. The order of formulas matches the UI checklist so comparisons remain stable across sessions.
Inputs accept numeric values and constrained enumerations only; no user supplied HTML is rendered. Clipboard, download, and query string features pass through predefined helpers that sanitize values and reject malformed data, and no secrets or credentials are stored.
How accurate are these estimates compared with a true max test?
For trained lifters performing three to six clean reps, the average usually lands within five percent of a supervised test; outside that window the spread grows, so validate with a lower rep session before changing your entire program.
Can I enter weights in pounds?
Yes. Choose pounds in the unit selector and all calculations, charts, and exports will reflect that unit, while the internal math still treats kilograms by converting behind the scenes.
What do I do if the formulas disagree?
Check the rep range first; if it sits above twelve, collect a lower rep set. Otherwise, keep the average for planning and watch how your next block responds before switching to a narrower formula set.
Is any data sent to a server when I enter my lift?
No. All computations run in the browser, and nothing is transmitted or stored remotely; only the optional query string holds your numbers, and you control when it is generated.
Does this cost anything or require an account?
The tool is free to use, does not request sign-ins, and needs no registration to copy, download, or share your results.
Why does the warning mention twelve reps?
The supporting research validated these regressions on efforts between one and twelve repetitions; beyond that point, technical fatigue and energy system differences inflate the projection, so the alert nudges you back into the validated envelope.
How should I interpret the percent table when planning a meet peak?
Use the higher percentages for heavier singles in the final weeks, the mid range for volume work, and track how close you can stay to the average while managing fatigue to judge readiness.
The formulas implemented trace back to widely cited strength science: the Epley progression published in collegiate strength manuals, Brzycki and Lander linear models from football cohorts, the Lombardi logarithmic curve, the Mayhew and Wathan regressions from bench press testing, and the O'Conner multiplier from National Strength and Conditioning Association guidance.
Percent table conventions mirror practical programming texts that load main work between 60 and 95 percent of one repetition maximum, keeping the experience aligned with established strength periodisation approaches.
All data stays on the client device unless you deliberately share a link or export; clear the query string before demonstrations to avoid exposing training history.