The short version
Only about 5% of the calcium in spinach is absorbed, compared with about 27% from milk. Kale, broccoli, and cabbage absorb about as well as milk but carry less calcium per serving (NIH Office of Dietary Supplements).
2 numbers on popular plant calcium lists are wrong: a sheet of nori has far less than 126 mg, and 5 dried figs have about 68 mg, not 135.
Tofu and sesame depend on how they're made. Calcium-set tofu and unhulled sesame are rich sources; other versions are much lower.
ODS says people who avoid dairy typically need fortified foods or supplements. Supplement questions are a referral.
Content versus absorption
Most adults aged 19 to 50 need 1,000 mg of calcium a day; women over 50 and everyone over 70 need 1,200 mg (ODS). Adults absorb about 25% of the calcium they eat, and that share keeps falling with age. It also falls as intake rises: about 45% of a 200 mg intake is absorbed, but only about 15% above 2,000 mg.
Plants add another layer. Oxalic acid and phytic acid bind calcium into salts the gut absorbs poorly. ODS lists spinach, collard greens, sweet potatoes, rhubarb, and beans as high in oxalate. Spinach is the classic trap: ½ cup boiled contains 123 mg, which looks impressive on a list, but only about 5% of it is absorbed.
Kale, broccoli, and cabbage are different. They're low in these compounds, and ODS says their calcium is about as bioavailable as milk's. The catch is quantity. Weaver, Proulx, and Heaney (1999) concluded that the amount of vegetables needed makes an all-plant diet impractical for most people unless fortified foods or supplements are included. Purdue's release on that work put it concretely: about 4.5 servings of broccoli to match the calcium in 1 cup of milk.
For people who eat a mixed diet, ODS notes that these interactions probably matter little. They matter most for clients who rely on plants alone.
Collards are worth a note because they look like kale's cousin and carry a lot of calcium on paper (about 268 mg per cooked cup in USDA FoodData Central). ODS lists them among the high-oxalate foods, so don't assume they behave like kale.
The corrected list
Values below are from USDA FoodData Central (FDC) or ODS, as noted.
Calcium-set tofu. Tofu is only a strong calcium source when it's made with a calcium salt, usually calcium sulfate. FDC lists regular tofu made with calcium sulfate at 434 mg per ½ cup, firm tofu made with calcium sulfate at 861 mg, and firm tofu made with calcium sulfate plus magnesium chloride (nigari) at 253 mg. That range is the point: check the ingredient list for calcium sulfate and the Nutrition Facts label for calcium.
Sesame: hulled versus unhulled. The 351 mg per ¼ cup figure is right only for whole, unhulled seeds (FDC: 975 mg per 100 g, about 88 mg per tablespoon). Hulled sesame kernels, the pale seeds most people buy, are 60 mg per 100 g dried, about 5 mg per tablespoon. The most common tahini, made from roasted kernels, has about 64 mg per tablespoon.
Fortified foods. Calcium-fortified soy milk has 299 mg per cup (ODS and FDC); unfortified soy milk has about 61 mg (FDC). Calcium-fortified orange juice has 349 mg per cup (ODS). Fortified foods absorb about as well as dairy, around 30% (ODS).
Low-oxalate greens. Kale, fresh and cooked, 94 mg per cup (ODS). Broccoli, cooked, about 31 mg per ½ cup (FDC). Bok choy, cooked, 158 mg per cup (FDC). Turnip greens, boiled, 99 mg per ½ cup (ODS).
Other plant foods. - Chia seeds: 76 mg per tablespoon (ODS) - Almonds: about 96 mg per ¼ cup, 76 mg per ounce (FDC) - Orange: 52 mg in a medium fruit (FDC) - Corn tortilla: 46 mg in a 6-inch tortilla (ODS) - Dried figs: about 14 mg each, so about 68 mg for 5 (FDC) - Nori: FDC lists laver, the seaweed nori is made from, at 70 mg per 100 g, or about 18 mg in 10 sheets. Nori is not a meaningful calcium source.
Using it with clients
The useful idea here is simple: what's on a list isn't always what the body gets. For a client who has moved away from dairy, or who was counting on spinach, that can feel freeing rather than discouraging, because it points to a few specific foods.
"Where do you think most of your calcium comes from right now?"
"Would it help if I shared what the NIH says about how well different plant foods are absorbed?"
"You were counting on spinach for calcium, and it turns out most of it isn't absorbed. What do you make of that?"
"Of the foods we looked at, which ones already fit the way you like to eat?"
Let the client choose the 1 or 2 changes that appeal to them, such as switching to a calcium-set tofu they already buy, or trying a fortified plant milk they'd enjoy. Label reading is a practical skill to explore together. You're sharing information from nationally recognized sources, not building a plan.
Where coaching stops
Coaches don't recommend calcium supplements or doses, and don't assess whether a client is meeting their needs. Refer questions about supplements, bone density, osteoporosis, medications, or a medical condition that affects absorption to the client's physician or a registered dietitian. Clients on fully plant-based diets who want help planning intake should see a registered dietitian.
Go deeper
The Nutrition Science Deep Dive package from One James is in development and will cover micronutrients, including absorption and what food composition data can and can't tell you.
References
National Institutes of Health, Office of Dietary Supplements. (n.d.). Calcium: Fact sheet for health professionals. Retrieved November 1, 2026, from https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
Purdue University News Service. (1999, December). Vegans likely short on calcium, experts say. https://www.purdue.edu/uns/html4ever/1999/9910.Weaver.vegans.html
U.S. Department of Agriculture, Agricultural Research Service. (2018). FoodData Central: SR Legacy [Data set]. https://fdc.nal.usda.gov/
Weaver, C. M., Proulx, W. R., & Heaney, R. (1999). Choices for achieving adequate dietary calcium with a vegetarian diet. The American Journal of Clinical Nutrition, 70(3 Suppl), 543S–548S. https://doi.org/10.1093/ajcn/70.3.543s
