Swing Weight & MgR/I
The single most important spec for how a racquet plays. Learn what swing weight means, how it's measured, and how to use it when choosing or customising a racquet.
Swing weight is the single most important specification for understanding how a racquet performs in play. Unlike static weight or balance point, swing weight measures resistance to angular acceleration during a swing — which is exactly what determines how a racquet feels when hitting a ball.
What Is Swing Weight?
Swing weight is the moment of inertia (MOI) of the racquet around a pivot point located 10 cm from the butt end of the handle. It is measured in kg·cm² and typically ranges from 280 to 390 for adult tennis racquets.
Formula:
I = Σ mᵢ · rᵢ²Moment of inertia: the sum of each mass element (mᵢ) multiplied by the square of its distance (rᵢ) from the pivot point 10 cm from the butt.
The 10 cm pivot approximates where the hand grips the racquet and the wrist acts as the axis of rotation during a swing.
MgR/I — The Normalised Metric
Swing weight in isolation doesn't tell you much without knowing the racquet's weight and balance. MgR/I (also called Recoil Weight or RW) normalises swing weight by the racquet's mass and balance:
Formula:
MgR/I = (M × g × R) / IM = mass (kg), g = 9.81 m/s², R = distance of balance point from the 10 cm pivot (m), I = swing weight (kg·m²). Result is dimensionless.
A higher MgR/I means the racquet is relatively more maneuverable compared to its stability. The Arcus fitting algorithm uses MgR/I alongside swing weight and twistweight to match racquets to player profiles.
Typical Values
| Swing Weight (kg·cm²) | Character | Typical Player | |---|---|---| | < 295 | Very light, fast | Junior, beginner, touch player | | 295–315 | Light | Intermediate baseliner, spin-focused | | 315–335 | Moderate | Club player, all-court game | | 335–355 | Stable, heavy | Advanced player, heavy ball | | > 355 | Very demanding | Tour-level, physically strong |
Values measured on a Babolat RDC at 10 cm from butt. ±3 kg·cm² variation between devices is normal.
How It Affects Play
Higher swing weight (>335):
- More power transferred to the ball on contact — more mass behind each shot
- Greater stability against off-centre hits and heavy incoming balls
- More arm load (shoulder and elbow fatigue faster)
- Slower swing speed; harder to generate spin on short backswings
Lower swing weight (<315):
- Easier to swing fast → more racquet head speed → more spin potential
- More maneuverable for volleys, defensive play, and quick exchanges
- Less power on groundstrokes — player must generate more themselves
- Less stable on heavy balls coming in
How It Is Measured
Swing weight is measured on a Babolat RDC or similar oscillation-based device. The racquet is clamped at the pivot point and set oscillating; the period of oscillation reveals the MOI.
Important caveats:
- Results can vary ±3–5 kg·cm² between different RDC units
- Within one machine, relative comparisons between racquets are reliable
- Specs published by manufacturers are often measured differently or rounded
Tip: Always match racquets within the same batch on the same RDC. Matching three racquets to within ±2 kg·cm² of each other gives consistent feel across your set.
Relationship to Other Specs
Swing weight is partly a function of weight and balance. A heavier racquet or a more head-heavy balance both increase swing weight. This is why balance point alone is insufficient — two racquets balanced identically can have very different swing weights if their mass distributions differ.
See also: Twistweight for stability on off-centre hits, Balance Point for static vs. dynamic spec interactions, and Lead Tape for how to adjust swing weight.