How Much Oxalate Is in Watermelon?
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 oxalate per 100g matter?
Per-100g values put every food on the same scale, which is handy when serving sizes differ a lot between foods — or when your portion doesn't match the standard serving. It lets you compare apples to apples on oxalate density. Watermelon comes in at 1 mg oxalate per 1 slice (Safe) in the measured database.
How accurate is the oxalate measurement?
The measurements use ion chromatography, the accepted reference method for oxalate. That means real lab values for each food rather than inferred numbers. Some natural variation exists between samples, but this is the strongest published data set. For context, Watermelon measures 1 mg per 1 slice, rated Safe.
How does this compare to other foods?
The ratings split at 25 mg (Safe) and 100 mg (Avoid), with 25-99 mg in the Caution band. For context against similar foods, the category pages on OxalateWatch rank every item in that group by oxalate. Watermelon comes in at 1 mg oxalate per 1 slice (Safe) in the measured database.