Strength Compatibility Calculator
How close two lifters have to be to share a bar without either one of them working around the other.
Compare like with like: the same lift, both taken to roughly the same effort. The app runs this per muscle group across your whole logged history rather than on one lift.
Example: your 100 kg lift against a partner's 85 kg is a 16.2 percent gap, just outside the 15 percent window the app matches within.
How this is worked out
It is a symmetric percentage difference: twice the gap between the two lifts, divided by their sum. That formula gives the same answer regardless of whose side you calculate from, which a plain percentage difference does not.
Symmetry is the whole reason for it. If you compared against one lifter's number, a 100 and a 120 would be 20 percent apart from one direction and 17 from the other, and a matching system that disagrees with itself about a pair is not a matching system.
Under 15 percent counts as a match. That is roughly the point where two people can work through the same sets without the plates changing every round, which is the practical thing being measured rather than an abstract closeness.
difference = 2 x |A - B| / (A + B) x 100
What it actually measures
Whether two people can train the same session without one of them compromising. Not who is stronger, and not whether you would get along.
The practical test is the bar. If your working weights are close, you spot each other meaningfully, you swap in without a full plate change, and the rest periods line up naturally. If they are far apart, every set becomes a reload and one of you is either sandbagging or overreaching.
This is why the number is about the ratio rather than the difference. Twenty kilos apart on a 200 kg deadlift is nothing. Twenty kilos apart on a 60 kg overhead press is two different training sessions.
Your match window
The range either side of your own lift that still counts as a match.
The window is not simply plus or minus 15 percent, because the formula compares against the average of the two lifters rather than against one of them. It works out slightly wider than a naive calculation would suggest, and it is symmetric: if they are in your window, you are in theirs.
| Your lift | Lightest match | Heaviest match | Window width |
|---|---|---|---|
| 40 kg (88 lb) | 34.4 kg (76 lb) | 46.5 kg (103 lb) | 12.1 kg (27 lb) |
| 60 kg (132 lb) | 51.6 kg (114 lb) | 69.7 kg (154 lb) | 18.1 kg (40 lb) |
| 80 kg (176 lb) | 68.8 kg (152 lb) | 93 kg (205 lb) | 24.2 kg (53 lb) |
| 100 kg (221 lb) | 86 kg (190 lb) | 116.2 kg (256 lb) | 30.2 kg (67 lb) |
| 120 kg (265 lb) | 103.3 kg (228 lb) | 139.5 kg (308 lb) | 36.2 kg (80 lb) |
| 140 kg (309 lb) | 120.5 kg (266 lb) | 162.7 kg (359 lb) | 42.2 kg (93 lb) |
The window either side of your lift that still counts as a match at the 15 percent threshold. It is not simply plus or minus that percentage: the formula is symmetric, so it compares against the average of the two lifters rather than against one of them.
Why 15 percent
Because it is roughly one plate. On most working weights a 15 percent gap is about the point where two lifters stop being able to alternate sets on the same loaded bar, which is the moment training together becomes taking turns.
It is a threshold, not a cliff. Two lifters at 16 percent will train together perfectly well; two at 40 percent will not, whatever the calculator says. The number exists to sort a list of strangers, not to referee a friendship.
How the app does it
On one lift this is a curiosity. What makes it useful is running it across every muscle group at once, from lifts both people have actually logged rather than numbers they typed into a profile.
Workout With Me computes a strength score per muscle group from your logged sets, compares it against everyone nearby, and shows a single match percentage next to each potential partner. Someone whose chest matches yours but whose legs are nowhere near will show up as the partial match they are.
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Key Takeaways
- The score is a symmetric percentage difference, so it gives the same answer whichever lifter you start from.
- Under 15 percent apart counts as a match, which is roughly the point where you can share a loaded bar.
- It measures whether you can train together, not who is stronger.
- The ratio matters, not the absolute gap: 20 kg apart is nothing on a deadlift and everything on an overhead press.
- The match window is slightly wider than plus or minus 15 percent, because the formula compares against the pair's average.
- The app runs this per muscle group across your logged history rather than on a single lift.
What is a Strength Compatibility?
Strength compatibility is how closely two lifters' working strengths align, expressed as a symmetric percentage difference between their scores. A low percentage means they can realistically train together on the same weights, spotting each other and alternating sets without reloading the bar between every round.
A gym buddy whose one rep max is within about 15 percent of yours — roughly one plate — can share a loaded bar and spot you safely, which is the window a strength compatibility score is built around.
Frequently Asked Questions
What is a good strength compatibility score?
Under 15 percent apart is a match. Under 5 percent means you can genuinely alternate sets on the same loaded bar. Past about 25 percent you are effectively training separately in the same room, which can still be good company but is not the same thing as training together.
Do I need to be the same strength as my gym partner?
No, just close enough that the bar does not need reloading between every set and that spotting is meaningful. A partner well outside your range can still be a good training partner for accountability and company. The score is about the mechanics of sharing equipment, not about who is worth training with.
How does Workout With Me calculate the match percentage?
It builds a strength score per muscle group from the sets you have actually logged, using estimated one rep maxes rather than self-reported numbers, then compares those scores against other users nearby with this same symmetric formula. The percentage shown next to a potential partner is the aggregate across muscle groups.
Does bodyweight matter for compatibility?
Not for this. Compatibility is about the weight on the bar, because that is what determines whether you can share it. A bodyweight adjusted comparison is a different question, and DOTS is the measure for that one.