Is Watermelon Safe for Kidney Stones? (Safe)
mg oxalate
per serving
Serving: 1 slice (280 g)
Verdict: 🟢 Safe
Per 100g: 3 mg
Data: Harvard T.H. Chan SPH (2024)
Here's the takeaway: Watermelon earns a Safe rating (🟢) at 1 mg oxalate per serving. Being under 25 mg means it fits comfortably in everyday eating. Keep your usual habits — adequate fluids and calcium in meals — and Watermelon poses no special concern.
Putting Watermelon in context: it lands well below the category average of 21 mg. In the database, 89% of fruits (101 of 113) fall in the 🟢 Safe group (under 25 mg oxalate/serving). The typical fruits here averages 21 mg oxalate per serving, so Watermelon runs 96% below that baseline. That places it among the lower-oxalate options in its category. Why this matters: the gap between two Safe foods can be wide — one may hold 5 mg oxalate while another sits at 24 mg. The lower one leaves more room in your day. See all fruits rated Safe for a full side-by-side.
Why does the safe threshold matter?
The 25 mg cutoff comes from clinical guidance for stone formers. Below it, a food's oxalate contribution is small enough not to move the needle for most patients. Harvard's 2024 lab data sits behind these figures — direct measurements, not estimates. For context, Watermelon measures 1 mg per 1 slice, rated Safe.
Can I eat this food every day?
For Safe foods (under 25 mg/serving), daily use is generally fine. Caution and Avoid foods work better as occasional items — rotate them with safer options so no single high-oxalate food becomes a habit. For context, Watermelon measures 1 mg per 1 slice, rated Safe.
Where does the oxalate data come from?
Harvard T.H. Chan School of Public Health (2024) via the OHF database. These are direct laboratory measurements — the most reliable oxalate data available for food. Watermelon comes in at 1 mg oxalate per 1 slice (Safe) in the measured database.
Should I also check sodium and calcium?
Definitely. Oxalate is only part of the story — high sodium raises calcium in urine, and dietary calcium (from food, not pills) binds oxalate in the gut. The food's main page lists both, so it's worth checking before you plan around it. Applied to Watermelon: 1 mg oxalate per 1 slice — Safe per Harvard (2024).