One rep max (1RM) calculator

Your 1RM (one-repetition maximum) is the most weight you can lift once with good form in a given exercise. Most strength programs set loads as a share of it, such as "5 × 5 at 80% of 1RM."

A true max test is demanding, carries injury risk and needs an experienced spotter. That's why many lifters estimate it instead: they lift a lighter weight for as many clean reps as they can and use a formula to work back to the max. That's also the safer choice for beginners and after a long break.

The calculator uses three formulas that are widely studied (w = weight, r = reps):

• Epley: 1RM = w × (1 + r ÷ 30)
• Brzycki: 1RM = w × 36 ÷ (37 − r)
• Lombardi: 1RM = w × r^0.10

The formulas agree closely at 2 to 6 reps and drift apart at higher counts. In a 2006 study by Reynolds and colleagues, estimates from fewer reps were more accurate. Above 10 reps the error grows quickly, so we show a warning above 12. The average of the three is a good starting point, but individual results also depend on the exercise, your training history and muscle fiber makeup.

You squatted 225 lb for 5 clean reps.

Formula	Calculation	Estimated 1RM
Epley	225 × (1 + 5 ÷ 30)	262.5 lb
Brzycki	225 × 36 ÷ 32	253.1 lb
Lombardi	225 × 5^0.10	264.3 lb
Average		260.0 lb

For a set of 8, the calculator works the formulas backward and suggests about 209 lb. Rounded to 205 lb on a 45 lb bar, that's 45 + 35 lb on each side.

The calculator lists training weights from 50% to 100% of your 1RM in 5% steps, and a second table shows which weight fits a given number of reps. As a general guide:

% of 1RM	Typical reps	Goal
85–100%	1–5	maximal strength
70–85%	6–12	muscle size (hypertrophy)
50–70%	12–20	muscular endurance, technique

These are averages. When you're tired, short on sleep or learning a new lift, fewer reps are normal.

• Warm up: start light and work up to your test weight gradually.
• Pick a weight you can lift 3 to 8 times: it gives an accurate estimate without lifting your max.
• Stop when form breaks down. Only clean reps count.
• Use a spotter or safety bars for bench press and squats.
• If you're new, focus on technique rather than maximums for the first few months.

If you have heart disease, high blood pressure, a recent injury or you're pregnant, talk to your doctor before heavy lifting. The WHO and the US Physical Activity Guidelines recommend muscle-strengthening activity on at least two days a week for adults.

The plate loader tells you which plates to put on each side of the bar to reach your target. In pounds it uses 45, 35, 25, 10, 5 and 2.5 lb plates; in kilograms, 25, 20, 15, 10, 5, 2.5 and 1.25 kg plates. You set the bar weight: a standard Olympic bar is 45 lb (20 kg), a women's bar 35 lb (15 kg).

If your plates can't make the exact weight, the calculator shows what's left over so you know whether to round up or down. You can pair the result with your heart rate zones and daily protein needs.