Tennis String Tension Calculator

The calculator subtracts 3 lbs for polyester and 4 lbs for Kevlar (versus a +2 lb boost for natural gut), because those materials are inherently stiffer and less elastic than gut or multifilament. Stringing a stiff material as tight as an elastic one produces a harsh, unforgiving stringbed that's harder on the arm, so the tension adjustment compensates for the material's own stiffness rather than aiming for the same feel across all string types.

Above 3,000 ft, the calculator adds up to 3 lbs based on how far altitude exceeds that threshold, because thinner air offers less resistance and lets the ball fly faster and further off the strings. A slightly tighter stringbed helps rein in that extra ball speed and restore a more normal feel for shot control, which is why the adjustment goes up rather than down.

The calculator subtracts 2 lbs for the baseliner/topspin style because looser strings deflect and "snap back" across the ball more during a topspin swing, which is the main mechanism that generates extra spin. Power hitters and serve-and-volleyers instead get boosted 2-3 lbs, since their games prioritize the control and directness a tighter stringbed provides over the added spin a looser one enables.

The range (recommended tension minus 2 to plus 2) reflects that stringing machines and calibration vary enough that a couple of pounds either way is unlikely to feel meaningfully different on court, so you don't need to hit the exact recommended number. The stiffness index multiplies your final clamped tension by a fixed stiffness factor for your chosen string material (from 0.7 for gut up to 1.3 for Kevlar), giving a single combined number where higher values mean a stiffer, more control-oriented stringbed with less inherent power.