How much oxalate a day: 50 or 100 mg?

By Oliver Silen · Updated November 2, 2026 · Not medical advice

Under 100 mg of oxalate a day is a good target for most calcium oxalate stone formers, and under 50 mg is the stricter one. The University of Chicago Kidney Stone Program puts it the same way: under 100 is good, under 50 is ideal [1].

Why this site grades against 50 mg

The grades here use the stricter number, so a food that's fine at 50 is fine at 100 too. Every food page also shows the share of a 100 mg day, so you can read it against whichever target your doctor gave you. A grade E food is more than a whole 50 mg day in one serving, and at least half of a 100 mg day, so check its number before counting it as an occasional food.

Who should aim for 50

High urine oxalate on a 24-hour test, after calcium intake is back to normal. Low calcium alone can raise urine oxalate [1].
Gut conditions that raise absorption, like gastric bypass, Crohn's disease or other fat malabsorption. These conditions can make the gut absorb far more of the oxalate eaten [5]. See oxalate after gastric bypass or with Crohn's.
Stones that keep coming back despite enough water and calcium.

What a normal day contains

In three Harvard cohorts of more than 240,000 people, average intake was 183 to 214 mg a day, and spinach alone supplied over 40% of it [2]. So most people get under 100 mg by cutting a handful of very high foods. One cup of raw spinach (grade E, 316 mg per 1 cup raw) is several days at either target.

Diet supplies roughly a quarter to two fifths of the oxalate in urine. In a controlled feeding study it ranged from 24% on a 10 mg diet to 42% on a 250 mg diet, and rose to 53% when calcium was cut [3]. The rest your body makes itself, which is one reason water and calcium matter as much as the oxalate count.

The other half of the plan

The American Urological Association's guideline puts fluid first, enough to make at least 2.5 liters of urine a day, and advises 1,000 to 1,200 mg of calcium a day from food rather than cutting it [4]. A low-oxalate target works alongside both.

Not sure you need a target at all? Do you need a low-oxalate diet covers the urine test. To check a day, use the oxalate calculator.