If you’ve been running long enough, you’ve asked the question. Maybe you typed it into a running sub-reddit at midnight, or asked a faster friend after a tempo run.
We get this question in various forms — more than almost any other. And we get it. All of us see the elites lining up at the start of a Major Marathon—lean, and seemingly gravity-defying. It’s quite natural to wonder: “If I lost two kilos, would I finally hit that PB?”. So, what should I weigh?
The short answer? There isn’t a single number that can be said as ‘racing weight’.
The term “Racing Weight” doesn’t refer to the lowest number you can possibly hit on a scale. Instead, it is the optimal weight at which you perform best. Think of your body like a car. To go fast, you need a powerful engine (muscles and aerobic capacity) and a light chassis (minimal non-functional mass). However, if you strip the chassis too much, you risk compromising the car’s structural integrity. Racing weight is about maximizing your power-to-weight ratio without sacrificing health, hormonal balance, or recovery.
Here’s the uncomfortable truth though: there is no single ideal weight for runners.
Your optimal racing weight depends on your body composition, your frame, your genetics, your training history, and even the distance you’re racing. Two runners standing at the same height can have wildly different optimal weights, one might race best at 62 kg while the other performs best at 68 kg. That is because their muscle mass, bone density, and fat distribution are different.
This is why BMI, the metric most people default to, is almost useless for runners. BMI is simply a ratio of weight to height. It tells you nothing about whether those kilograms are muscle, bone, or fat. A strong, well-built runner with a BMI of 24 might be leaner and faster than a lighter runner with a BMI of 21 who carries more body fat relative to muscle.
Body fat percentage is a far more meaningful number than body weight. It measures what actually matters i.e., How much of your mass is working for you (muscle, bone, organs) versus sitting along for the ride (excess fat).
It is dangerous and usually counterproductive for recreational runners to compare their bodies to elite professionals.
For context, here’s a rough comparison of typical body fat ranges:
| Elite Runners | Competitive Recreational | Casual Recreational | |
|---|---|---|---|
| Men | 5–8% | 10–15% | 15–20% |
| Women | 12–16% | 18–23% | 20–28% |
In his book ‘Racing Weight’, Matt Fitzgerald outlines the approach to determine your racing weight. We’ve taken the concepts from the Racing Weight framework and built a Racing Weight Calculator on RunStrong to give you a personalised starting point.
1. Identify Your Profile
Because physiology varies, you must start with your gender, age group, and current weight. This provides the baseline for where you stand relative to other runners in your demographic.
2. Find Your Current Body Composition
Weight alone is a “dumb” metric—it doesn’t distinguish between muscle (the engine) and fat. To get an accurate calculation, you need your current Body Fat Percentage (BF%). You can find this via:
3. Set a Realistic Goal (The Percentile Method)
Rather than picking a random weight goal, you should pick a Target Percentile.
A rough rule of thumb: losing about 1 kg of body weight (read it as fat) can improve your marathon time by approximately 2–3 minutes, depending on your pace.
The Calculation
Once you know your lean mass and your target body fat percentage, the math is simple. Our calculator uses the following logic:
Racing Weight = [Current Weight × (100% – Current Fat %)] ÷ (100% – Target Fat %)
If you currently weigh 80 kg with 20% body fat and your goal is 15% body fat:
This means your estimated Racing Weight is 75.3 kg.
Try the RunStrong Racing Weight Calculator
Your best weight is the one that allows you to train hard, recover well, and feel strong. If reaching a “target weight” makes you feel sluggish, irritable, or prone to injury, you’ve likely passed your optimal point.
The RunStrong calculator is an estimate based on population norms—not a prescription. Treat it as a compass to guide your training and nutrition, but always prioritize how you feel on the road over the number on the screen.
Have you tried reaching a specific racing weight before? Or you have any questions to us on Racing weight, Let us know in the RunStrong forum!
This article is compiled by Team GeeksOnFeet for the love of running. If you have any questions or suggestions, feel free to reach out to us at [email protected].