Onigiri Rice Ball Calculator
Set the number of onigiri, size, and filling type to get precise cooked rice, dry rice, water, nori strips, filling, and shaping salt quantities.
Onigiri Settings
Salted or grilled salmon flakes, mild and rich
Onigiri Size
8 Standard (100g) onigiri with Salmon (salted)
800 g cooked rice needed
372 g dry rice • 1.9 cups dry
Shaping Technique
Wet your hands with cold water and rub a pinch of salt on your palms before handling each onigiri. This prevents sticking and seasons the exterior. Work quickly while the rice is still warm — cold rice is harder to compress into a cohesive shape. Apply firm, even pressure forming a triangle: base first, then two sides.
Size Reference
| Size | Cooked Rice | Filling | Nori Strips | Salt |
|---|---|---|---|---|
| Small (70g) | 70 g | 10 g | 1 | 0.5 g |
| Standard (100g) | 100 g | 15 g | 1 | 0.7 g |
| Large (130g) | 130 g | 20 g | 1.5 | 1 g |
What Makes a Perfect Onigiri
Onigiri (also called omusubi) are Japanese rice balls — one of the most practical foods ever invented. They require no utensils, travel well, keep for hours, and can be filled with virtually any ingredient. Despite their simplicity, the difference between a mediocre and exceptional onigiri lies in rice variety selection, proper seasoning, and shaping technique.
The triangular shape is the most common form in Japan, though cylindrical (tawara) and round (maru) shapes are also traditional. The triangle represents a spiritual symbol in some Japanese traditions, though most contemporary onigiri are triangular simply because the shape is structurally stable and easy to wrap.
Rice Variety: Short-Grain Koshihikari
Koshihikari is the undisputed premium variety for onigiri. Grown primarily in Niigata, Akita, and Toyama prefectures, Koshihikari rice has a distinctive sweetness, glossy appearance, and ideal cohesion when shaped. Its high amylopectin content creates the necessary stickiness for the rice to hold together under hand pressure without being gluey.
Outside Japan, Calrose rice grown in California is the most widely available short-grain variety with comparable cooking properties. Akitakomachi is another excellent option with a slightly firmer texture than Koshihikari. Avoid medium-grain American rice varieties, which lack the starch profile needed for proper onigiri texture.
Water Ratio for Onigiri Rice
Cook onigiri rice at a 1:1.1 ratio of rice to water by volume (the same as sushi rice). This produces slightly firmer rice than standard Japanese cooking, which helps the onigiri hold its shape without becoming dense. The firmness should be detectable when you press the rice — slightly chewy but fully cooked, not crunchy.
If using a rice cooker, the automatic setting for white rice works well for onigiri rice. After cooking, let the rice steam on the warm setting for 10 minutes with the lid closed before using. This equilibrates moisture throughout each grain and makes shaping easier.
Salt: The Essential Seasoning
Two types of salt are used in onigiri preparation. The first is shaping salt: a small amount of fine salt rubbed on damp hands before shaping each ball. This seasons the exterior of the rice (which becomes the surface you eat first), prevents sticking, and gives the onigiri its characteristic savory exterior. Use approximately 1g of salt per onigiri for shaping.
The second application is rice seasoning: a small amount of salt mixed into the entire batch of cooked rice before portioning. This interior seasoning is lighter, typically 0.5-0.7g per standard onigiri equivalent, mixed into the warm rice. Together, these two salt applications create a flavor that is distinctly seasoned without being overtly salty.
Filling Types and Preparation
Umeboshi (Pickled Plum)
The most traditional onigiri filling. A single small umeboshi is placed whole in the center of each rice ball. Umeboshi is intensely sour and salty, so no additional seasoning is needed when using it. Its antibacterial properties also extend the shelf life of the onigiri slightly. Remove the pit before serving if using whole umeboshi in children's onigiri.
Salted Salmon (Shiozake)
Cook salted salmon (or season fresh salmon with salt and grill), then flake it into small pieces. Approximately 15g of salmon flakes per standard onigiri is the right amount — enough to find filling in every bite but not so much that it falls out when pressed. Remove all small bones before using as filling.
Tuna Mayo
Drain canned tuna thoroughly, then mix with Japanese mayonnaise (Kewpie brand) at a ratio of approximately 3:1 tuna to mayo by weight. Season with a small amount of soy sauce. This is the most popular convenience store (konbini) onigiri filling in Japan. Use 15g per standard onigiri. Because mayo is perishable, tuna mayo onigiri should be eaten within 4 hours at room temperature.
Simmered Kombu (Tsukudani Kombu)
Braised kelp strips simmered in soy sauce, mirin, and sake until thick and glossy. Kombu filling is deeply savory with a seaweed umami that complements plain rice exceptionally well. It keeps longer than fresh protein fillings and is suitable for all-day bento boxes.
Shaping Technique: Hand vs. Mold
Hand-shaping is the traditional method and produces the best texture. Wet your hands with cold water, rub salt on your palms, and place a 100g portion of warm (not hot) rice in one hand. Make a small well with your thumb, place the filling, then close the rice over it. Cup your hands firmly around the ball and apply equal pressure from three sides, rotating slightly to form a compact triangle. Repeat 3-4 firm compressions — this is enough to bind the rice without crushing the grains.
Onigiri molds (available in plastic triangle shapes) are more consistent for beginners and produce professional-looking results. Wet the mold interior with water before filling, press the bottom layer of rice in, add filling, top with more rice, and press the lid firmly. The density from molds is slightly higher than hand-shaped, which can make the rice feel dense. Experiment with how firmly you press.
Nori: Wrapping Styles
Nori wrapping serves two purposes: it improves structural integrity and provides a non-sticky surface for holding. In Japan, the preferred style for bento is the individually wrapped nori that is attached just before eating, keeping the nori crisp. The wrapping consists of a strip of nori with a plastic separator that divides it from the rice until you tear the sides and pull out the separator.
For immediate consumption, wrap a strip of nori (approximately 3cm x 8cm for a standard onigiri) around the base of the triangle, covering roughly the bottom third. This provides a grip point without wrapping the entire rice surface. Full-wrap style (covering the entire exterior) is also popular but makes the nori absorb moisture from the rice faster.
| Size | Rice (cooked) | Filling | Nori Strips | Salt (hands) | Best For |
|---|---|---|---|---|---|
| Small (70g) | 70g | 10g | 1 strip | ~0.5g | Children, side serving |
| Standard (100g) | 100g | 15g | 1 strip | ~0.7g | Adult bento, snack |
| Large (130g) | 130g | 20g | 1.5 strips | ~1g | Lunch, hungry appetite |
Frequently Asked Questions
A standard onigiri contains 100g of cooked short-grain rice. Small onigiri use 70g and large ones use 130g. The rice should be warm (not hot) when shaping — too hot burns hands, too cold makes the rice break apart.
Japanese short-grain rice (Koshihikari, Akitakomachi, or Calrose) is essential for onigiri. The high amylopectin content makes the rice sticky enough to hold its shape when pressed. Season the rice lightly with salt before shaping — about 0.5-1g per onigiri rubbed on your wet hands.
Wet your hands with cold water and rub a pinch of salt (about 1g) on your palms. Place a portion of warm rice on one hand, make a small indentation, add filling, then fold the rice over. Cup both hands around the rice and apply firm pressure from three sides, rotating to form a triangle. Repeat 3-4 times to compact the rice.
A standard 100g onigiri holds about 15g of filling, small onigiri hold 10g, and large ones hold 20g. The filling should be centered to appear when the first bite is taken.
Plain onigiri (without nori) keep at room temperature for 4-6 hours wrapped in plastic wrap. Wrap nori separately and attach just before eating to maintain crispness. Onigiri with moist fillings (tuna mayo) should be consumed within 4 hours.
Wrap a strip of nori around the base of the triangle after shaping. For bento boxes meant to stay crisp, use individually wrapped nori packets that slide off just before eating. Alternatively, wrap the entire onigiri in a full half sheet of nori for a fully wrapped style.
- Japan Rice Council — Koshihikari variety guide
- Andoh, E. (2012). Washoku: Recipes from the Japanese Home Kitchen. Ten Speed Press.
- USDA FoodData Central — short-grain white rice data