NotesResearch note
How Racquet estimates string health
Strings don’t come with a fuel gauge. Here is the rule Racquet uses instead: published stringing guidance, tuned to how you play, and honest about what it can’t know.
On this page
Strings start losing tension as soon as they’re strung, and keep losing it with every hit and every week in the bag. Most players only notice when their shots stop doing what they expect. Racquet’s job is to notice earlier.
Key points
- Two clocksStrings are due after a number of hours of play or a length of time in the frame, whichever comes first. The other clock adds half its weight.
- Published guidanceA regular player’s polyester is due at about 25 hours or 4 months; natural gut at about 50 hours or 8 months.
- Tuned to youCasual players get 1.3 times the hours, competitive players 0.6 times, and restringing sooner for arm comfort takes 20% off.
- An estimate, not a measurementRacquet works from what you log. It never measures tension, and it says so wherever it shows a number.
Why an estimate
You can’t see string wear from the outside. Strings look much the same at ten hours as at forty, and a tension reading needs a meter and the racquet out of the bag. What players do know is how much they play, and when they last restrung.
So that’s what Racquet uses. You log sessions as you play, or import tennis workouts from Apple Health, and record each restring. From those, the type of string and how you play, Racquet estimates how much life is left: a percentage, one of four states, and the inputs that produced it.
The rule
Advice on restringing comes in two forms: after so many hours of play, or after so many months. Tennis Warehouse University’s lab tests show strings losing tension from the moment they’re strung, played or not. Babolat suggests restringing about every three months even if the racquet barely leaves the bag; Wilson suggests every six months for recreational players and every month for competitive ones.
Racquet runs both clocks at once. Play counts towards the hours a player like you is usually advised to get from a string; time counts towards a limit for that string. Whichever is further along sets the estimate, and the other adds half of its own progress, so heavy play on old strings comes due sooner than either clock alone would say.
A regular player with 3 h a week of polyester, 25% of it matches, is due soon in 5 weeks and should restring by 7 weeks. Play gets there first; string age adds to it.
Show the values as a table
| Week | Estimate | Play alone | Age alone | State |
|---|---|---|---|---|
| 0 | 100% | 100% | 100% | Fresh |
| 1 | 90% | 90% | 100% | Fresh |
| 2 | 80% | 80% | 100% | Fresh |
| 3 | 70% | 70% | 100% | Fresh |
| 4 | 57% | 60% | 94% | Monitoring |
| 5 | 45% | 50% | 89% | Monitoring |
| 6 | 32% | 40% | 83% | Due soon |
| 7 | 19% | 30% | 77% | Restring recommended |
| 8 | 6% | 20% | 72% | Restring recommended |
| 9 | 0% | 10% | 66% | Restring recommended |
| 10 | 0% | 0% | 60% | Restring recommended |
Two clocks, combined
Figure 2 shows every combination of hours played and days since stringing at once. Along the bottom only play counts; up the left side only age counts. The dashed corner is where strings would be due if only the leading clock counted. The solid 20% line bows inside it: with both clocks running, a restring comes sooner.
Age only starts to count 21 days after stringing. Until then, only play moves the estimate.
Polyester for a regular player: restring at 25 hours of play or 120 days, whichever comes first. With both clocks running it comes sooner: at 60 days old, 20 hours is enough.
Show the values as a table
| Days ↓ / hours → | 0 h | 5 h | 10 h | 15 h | 20 h | 25 h | 30 h | 35 h |
|---|---|---|---|---|---|---|---|---|
| 0 days | 100% | 84% | 68% | 52% | 36% | 20% | 4% | 0% |
| 30 days | 93% | 80% | 64% | 48% | 32% | 16% | 0% | 0% |
| 60 days | 68% | 60% | 52% | 36% | 20% | 4% | 0% | 0% |
| 90 days | 44% | 36% | 28% | 20% | 8% | 0% | 0% | 0% |
| 120 days | 20% | 12% | 4% | 0% | 0% | 0% | 0% | 0% |
| 150 days | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
Strings compared
Different strings last differently. Polyester runs out first on both clocks and natural gut lasts longest. These are Racquet’s defaults, set from the published guidance listed below.
Hours of play to “Restring recommended”
Dot: regular player. Band: competitive (×0.6) to casual (×1.3).
Or this long in the frame
The same for every player, from published guidance.
Show the values as a table
| Strings | Competitive | Regular | Casual | Time limit |
|---|---|---|---|---|
| Polyester | 15 h | 25 h | 33 h | 120 days |
| Hybrid | 18 h | 30 h | 39 h | 150 days |
| Multifilament | 24 h | 40 h | 52 h | 180 days |
| Synthetic gut | 21 h | 35 h | 46 h | 180 days |
| Natural gut | 30 h | 50 h | 65 h | 240 days |
How you play scales the hours. Casual players, who hit socially about once a week, get 1.3 times the hours. Competitive players, who play matches, leagues or training and hit hard, get 0.6 times. If you choose to restring sooner for arm comfort, Racquet takes 20% off. Match minutes count 1.15 times, for the intensity of points played for real.
From a number to advice
The percentage turns into one of four states. They’re the same everywhere Racquet shows strings: on Home, the racquet sheet, the widgets and in reminders.
- Below 20%Restring recommendedPast the guidance for your strings and how you play.
- 20–39%Due soonBook a restring. An optional reminder arrives the next morning.
- 40–69%MonitoringStill fine to play. Racquet keeps an eye on them.
- 70–100%FreshAbout as good as the day they went in.
Each estimate also has a confidence. It’s low when the string type is unknown, medium before you’ve logged any play on the current strings, and high once you have. If you turn on reminders, Racquet sends one the morning after a racquet reaches Due soon, and again at Restring recommended.
The formula
For one string job, from the day it went in:
- hours
- h = practice + 1.15 × matches
- target
- H = string hours × level × 0.8 if restringing sooner
- play
- p = 0.8 × h ÷ H
- age
- a = 0.8 × max(0, days − 21) ÷ (time limit − 21)
- condition
- 1 − (max(p, a) + 0.5 × min(p, a)), kept between 0 and 1
The 0.8 is the distance from 100% to where Restring recommended begins, at 20%. A string that reaches its hours, or its time limit, on its own lands exactly on that line.
Worked example
A regular player’s polyester, six weeks after stringing. They play 3 hours a week, a quarter of it matches.
- Hours: 13.5 practice + 1.15 × 4.5 matches = 18.7 h, of a 25 h target
- Play: 0.8 × 18.7 ÷ 25 = 0.60
- Age: 0.8 × (42 − 21) ÷ (120 − 21) = 0.17
- Condition: 1 − (0.60 + 0.5 × 0.17) = 0.32
32%: Due soon.
What it can’t know
- Tension and stiffness. Racquet doesn’t measure them. Strings of the same type differ: gauge, tension, brand and the stringing all change how quickly they lose tension.
- Your conditions. Heat, the court surface and how much spin you hit can all speed wear up. None of them are inputs.
- Play you don’t log. Sessions that aren’t recorded, or imported from Apple Health, don’t count.
- Every player. The defaults come from published guidance, not from testing your strings. We’ll adjust them as we compare estimates with what players and stringers report.
If your strings feel dead before the estimate says so, trust that.
Sources
Tennis Warehouse UniversityLab tests on how strings lose tension.
TennisnerdPolyester about every two months, at four hours of play a week.
Tennis CompanionTwice a year for each session you play a week.
WilsonEvery six months for recreational players, monthly for competitive ones.
BabolatAbout every three months, even when the racquet isn’t played.
Changelog
- Strings are due after a number of hours or a length of time, whichever comes first, with defaults from published guidance. Adds how you play and restringing sooner for arm comfort.
- Wear grew in a straight line with play towards a fixed number of hours for each string, from 12 for polyester to 36 for natural gut, with age adding wear after 30 days.
Cite this note
Racquet (2026). How Racquet estimates string health. Racquet Notes, 26 October 2026. https://getracquet.com/notes/string-health
See it on your racquets.
Racquet runs this estimate on every string job you log, and tells you what changed it.