1RM(最大挙上重量)計算ツール

What is a one rep max?

Your one rep max (1RM) is the heaviest weight you can lift correctly for exactly one repetition of a given lift. Strength programs, competition planning, and most percentage-based templates all assume you know — at least roughly — what that number is. Tested 1RMs are accurate but expensive: they require a peaking week, a focused session, and they carry meaningful injury risk if your technique breaks down. Estimated 1RMs, calculated from a submaximal set, give you most of the benefit at a fraction of the cost.

This calculator runs the six most-cited 1RM formulas in the strength-and-conditioning literature side by side, then averages them so you can see both the consensus and the spread. Wide spread? Your set was probably outside the formulas’ tested range — typically 1 to 10 reps. Narrow spread? Trust the average.

The six formulas, explained

All six expect a weight w and a rep count r. Each was fit to a different data set, which is why they disagree slightly.

Epley

1RM = w × (1 + r / 30)

Brian Epley’s 1985 formula assumes each rep above one adds roughly 3.3% to the load. It tends to slightly overestimate for sets above six reps, but it is the most popular formula precisely because the math is trivial to do in your head: ten reps is roughly +33%.

Brzycki

1RM = w × 36 / (37 − r)

Matt Brzycki’s 1993 formula is the standard rival to Epley. It diverges as reps climb and slightly underestimates at higher reps. For sets between three and seven reps, Brzycki and Epley typically agree within 1–2%.

Lombardi

1RM = w × r^0.10

Lombardi’s power-law fit is gentler at the top end. For low reps it agrees with Epley; for sets of ten or more it produces noticeably lower estimates and thereby tracks reality better when fatigue dominates.

Mayhew

1RM = w × 100 / (52.2 + 41.9 × e^(-0.055 × r))

Mayhew et al.’s exponential decay was fit to bench-press data. It produces conservative estimates above about six reps and is often the lowest of the six in the 8–10 rep range.

O’Conner

1RM = w × (1 + 0.025 × r)

O’Conner’s formula is essentially Epley with a smaller per-rep increment (2.5% instead of ~3.3%). It is the most conservative of the lot and is a useful sanity check when other formulas seem optimistic.

Wathan

1RM = w × 100 / (48.8 + 53.8 × e^(-0.075 × r))

Wathan’s exponential fit, like Mayhew’s, was bench-derived. It often sits between Brzycki and Mayhew in the 5–8 rep window.

A worked example

Suppose you bench-pressed 100 kg for 5 clean reps.

• Epley: 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg
• Brzycki: 100 × 36 / 32 = 112.5 kg
• Lombardi: 100 × 5^0.10 = 100 × 1.1746 = 117.5 kg
• Mayhew: 100 × 100 / (52.2 + 41.9 × e^−0.275) = 100 × 100 / (52.2 + 31.83) = 119.0 kg
• O’Conner: 100 × 1.125 = 112.5 kg
• Wathan: 100 × 100 / (48.8 + 53.8 × e^−0.375) = 100 × 100 / (48.8 + 36.97) = 116.6 kg

Average: 115.8 kg. The six estimates span 6.5 kg, or about 6%. That spread is normal for a five-rep set. If you saw a 15-kg spread, your reps were probably either too few (less than three) or too many (more than ten) for the formulas to interpolate cleanly.

How to use this calculator

1. Pick a recent single working set — ideally a top set from your last training session, performed close to failure but not to absolute failure. The math is more reliable when at least one rep was left in reserve.
2. Choose metric or imperial. The result auto-converts if you flip the toggle.
3. Enter the weight lifted and the clean rep count. Don’t count the rep you grinded out for fifteen seconds — that’s a near-failure rep with technique drift, and it pulls the estimate up.
4. Read the average as your working 1RM. Inspect the per-formula table if the spread looks suspicious.
5. Use the percentage table below the result to seed a 5×5, 5/3/1, or any percent-based program.

When the calculator is wrong

The six formulas were validated on bench-press sets in the 1- to 10-rep range. Outside that band, expect noise:

• Singles and doubles. All six formulas converge here, but error is dominated by your warm-up and central nervous system readiness, not the math. A single at 95% with great bar speed and a single at 95% with a grinder leave you at very different absolute strengths.
• Fifteen reps and beyond. Cardiovascular fatigue and form drift dominate. The formulas underestimate true 1RM for genuinely strong-endurance sets and overestimate for technique-limited sets.
• Lifts with steep strength curves. Deadlifts off the floor, sumo deadlifts, and partial-range movements break the formulas more than squats and bench. Treat the result as a starting anchor.
• Severe deloads or returns from injury. Your nervous system is the limiter, not your tissue. The formulas don’t model that. Test conservatively.

Programming with your estimated 1RM

A clean, repeatable workflow:

1. Estimate your 1RM at the end of each training block.
2. Plug the average into your program’s percentage table.
3. Adjust by ±2.5 kg in the first week of the new block based on bar feel and rep performance.
4. Test the estimate with an AMRAP (as-many-reps-as-possible) on the last working set of the block; recompute and continue.

This loop — estimate, train, AMRAP, re-estimate — is the backbone of progressive overload programming and lets you scale weights without ever true-testing.