// FREE CALCULATOR //

One Rep Max Calculator

Enter the weight and reps from a hard set to get your estimated one-rep max (1RM): the heaviest single you could likely lift. It uses the Epley formula, weight × (1 + reps ÷ 30), which is the one the IronLedger app uses for your records, with Brzycki beside it.

Epley or Brzyckikg or lbNo sign-upSame maths as the app

// ESTIMATED 1RM //

262.5 lb

From 225 lb × 5 with Epley. Brzycki gives 253.1 lb.

Percentages of a 262.5 lb max, rounded to 0.5
% of 1RM	Load (lb)
100%	262.5
95%	249.5
90%	236.5
85%	223
80%	210
75%	197
70%	184
65%	170.5
60%	157.5
55%	144.5
50%	131.5

What Epley predicts you can lift for each rep count
Reps	Load (lb)	% of 1RM
1	262.5	100%
2	246	93.8%
3	238.5	90.9%
4	231.5	88.2%
5	225	85.7%
6	219	83.3%
7	213	81.1%
8	207	78.9%
9	202	76.9%
10	197	75%
11	192	73.2%
12	187.5	71.4%

// THE MATH, IN THE OPEN //

Two formulas, written out.

// EPLEY //

1RM = weight × (1 + reps ÷ 30)

// BRZYCKI //

1RM = weight × 36 ÷ (37 − reps)

Worked example, 100 kg × 5: Epley gives 100 × (1 + 5 ÷ 30) = 116.7 kg; Brzycki gives 100 × 36 ÷ 32 = 112.5 kg. A single is the weight itself in both.

The tables under the calculator run the formula backwards. The percentage table is your estimate multiplied out, for programs written in percentages. The rep table is the load the formula expects you to manage for each rep count: the same projection as the rep-max table in IronLedger’s Analytics, rounded to the nearest 0.5.

// WHEN TO TRUST IT //

A good estimate needs a good set.

Use 2 to 10 reps

Estimates from heavier sets hold up better. In Reynolds and colleagues’ study, a 5-rep max predicted the 1RM more accurately than a 10- or 20-rep max. Above 10 reps this calculator flags the result as a rough guide.

Take the set close to failure

The formulas assume the set was the most reps you could do. If you stopped with reps left, the estimate comes out low. Add those reps back with the RPE calculator, which reads RPE as reps in reserve.

The formulas part ways as reps rise

Epley and Brzycki agree exactly at 10 reps. Below that, Brzycki is lower; above it, Brzycki is higher, and the gap grows quickly: for 100 kg × 15, Epley says 150 kg and Brzycki 163.6 kg.

An estimate is not a test

It tells you roughly where your strength is and which way it is moving. It does not promise what you would lift on a maximal attempt on the day, and it should not be used to pick a competition opener.

// PUTTING IT TO WORK //

From a max to a training plan.

Most percentage-based programs need a max to work from. Here is where this number goes.

Percentage programs

Programs such as 5/3/1 prescribe each set as a percentage of a training max, a number set below your estimate on purpose. IronLedger’s 5/3/1 setup uses 90% of a tested or estimated 1RM by default.

Tracking progress

An estimated 1RM lets you compare a set of 8 in one block with a set of 3 in the next. That is why IronLedger charts it per lift; see how estimated 1RM works for the longer version.

Choosing loads by feel

If your program gives a target RPE instead of a percentage, use the RPE calculator to turn your max and the target into a starting load.

// DIRECT ANSWERS //

Questions lifters ask.

How do you calculate a one rep max?

Do a set of a weight you can lift for 2 to 10 good reps, taken close to failure, then apply a formula. With Epley, 1RM = weight × (1 + reps ÷ 30), so 100 kg for 5 reps estimates 116.7 kg. The only way to know a true 1RM is to test a single, which needs a proper warm-up and a spotter.

What is the difference between Epley and Brzycki?

Epley is weight × (1 + reps ÷ 30); Brzycki is weight × 36 ÷ (37 − reps). They agree exactly at 10 reps. Below 10 reps Brzycki gives the lower estimate (112.5 kg against Epley’s 116.7 kg for 100 kg × 5), and above 10 reps it gives the higher one.

How accurate is a one rep max calculator?

It is close when the set is heavy and close to failure, and less reliable as reps climb. In one study of the bench press and leg press, estimates from a 5-rep max were more accurate than from a 10- or 20-rep max, and the authors advised using no more than 10 reps (Reynolds et al., 2006).

Why does a single return the same weight?

Because a single is a 1RM as lifted. This calculator and the IronLedger app both treat one rep as the weight itself. Applying Epley’s formula to one rep would add 3.3%, which would make a single look stronger than it was.

What is a training max?

A deliberately conservative number that a program takes its percentages from, so the early weeks feel manageable and there is room to progress. IronLedger’s 5/3/1 setup uses 90% of a tested or estimated 1RM by default, and you can change it.

Does IronLedger work this out for me?

Yes. IronLedger estimates a 1RM from every set you log with the same Epley formula, keeps your best for each lift as a record and charts the trend. The app rounds the stored record to a whole number; this calculator shows one decimal.

// SOURCES //

Where the maths comes from.

Let the app do this on every set

IronLedger estimates your 1RM from every set you log, keeps your best for each lift as a record and charts it over time, with the same Epley formula. Free, with no subscription. iPhone now; Android is in closed testing.

Get IronLedger free on iOS

Use it from an AI assistant

The same calculation is a free JSON API at /api/tools/one-rep-max and a tool on the IronLedger MCP server, so an assistant can run it and link back to this page with your numbers.

API and MCP details

// MORE TOOLS //