Sous Vide Thickness Calculator

Thermal diffusivity (α) is a material property describing how quickly temperature changes propagate through a material. It equals thermal conductivity divided by the product of density and specific heat: α = k / (ρ × Cp). For most meat and fish, α ≈ 0.12–0.14 mm²/s. Foods with higher water content (vegetables, fish) have slightly higher thermal diffusivity and heat faster. Foods with higher fat content have lower thermal diffusivity and heat more slowly. Knowing α allows exact calculation of heating times via Fourier's law, which is the basis of this calculator.

Yes, significantly for thick cuts. For a slab (flat steak), heat enters only from the top and bottom surfaces — the thermal path to center is the half-thickness. For a cylinder (tenderloin), heat enters from all sides radially, and analytical solutions (Bessel functions) show the center heats approximately 25% faster than an equivalent-diameter slab. For a sphere, convergent heat flow from all directions means the center heats approximately 40% faster than a slab. For thin items (below 20 mm), the shape effect is small. For items above 50 mm, using the correct shape factor can save 30–60 minutes of cooking time.

Always measure the thickest part of the cut — this determines the minimum cooking time, as the center of the thickest section is the last to reach temperature. For a chicken breast that tapers from 35 mm to 15 mm, use 35 mm as your thickness (alternatively, pound it flat to even thickness for more uniform cooking). For a bone-in cut, measure the meat thickness on the side away from the bone, as bones conduct heat differently than muscle. For rolled roasts, measure the overall diameter as a cylinder.

Stacking is generally not recommended because stacked items effectively increase thickness and prevent water circulation between pieces. A bag with two 25 mm steaks stacked will heat like a 50 mm slab at the contact zone — requiring double the time for the interior surfaces to reach temperature. If you must cook multiple pieces in one bag, arrange them in a single layer without overlap, or use multiple bags. For items like chicken wings or small vegetables that are too thin to stack significantly, multiple pieces per bag is acceptable if they are not tightly bunched.

Fish muscle has a fundamentally different protein structure than red meat. Fish myomeres (muscle segments) are separated by thin collagen sheets that convert to gelatin very quickly at cooking temperatures. At 45–52°C, this conversion begins within 30–45 minutes and accelerates with time. After 60–90 minutes at temperature, fish becomes overly soft, loses its flaky texture, and can taste mushy. This is in contrast to beef, where collagen conversion (at 60–65°C) actually improves texture of tough cuts over many hours. For fish, timing precision is more important than for meat.

Items thinner than 10–15 mm heat so quickly in a water bath that the minimum cook time is dominated by pasteurization holding time rather than heat diffusion. Very thin items (below 10 mm) like shrimp, thin fish fillets, or vegetable slices can be cooked conventionally in 2–5 minutes and do not benefit significantly from sous vide's primary advantage (preventing overcooking through precise temperature control). Sous vide is most valuable for items 20 mm and above, where the conventional technique makes it very difficult to maintain a specific internal temperature across the entire cross-section.

The volume of the water bath does not significantly affect the time for the food center to reach temperature, as long as the circulator can maintain the set temperature within ±0.5°C throughout cooking. What matters is the thermal mass of the food relative to the water bath — larger food loads can temporarily lower bath temperature if added at once (cold shock). Allow the bath to recover to set temperature before calculating cook time. For large batch cooking, preheat your circulator and add food gradually or increase the bath temperature by 1–2°C while loading.

Starting temperature affects the total time needed to bring the food center from initial to bath temperature. The temperature difference between starting food temperature and bath temperature directly scales heating time. Going from 4°C (fridge) vs. 20°C (room temperature) to a 57°C bath represents a 53°C vs. 37°C temperature rise — about 43% more time needed from the fridge. Frozen food at -18°C requires a 75°C rise to reach the same bath temperature plus the latent heat of thawing ice — explaining the approximately 60 minute additional time required for frozen food.

Heating time is the time for the food center to physically reach the bath temperature. Pasteurization time is the additional holding time at temperature needed to reduce pathogen load to safe levels. At most sous vide temperatures, pasteurization requires the food to be held at the target temperature for a specific duration after reaching it: at 60°C, chicken requires 35 minutes; at 63°C, 8 minutes; at 68°C, 3 minutes (USDA 7-log reduction). For beef and pork at common sous vide temperatures (57–63°C), pasteurization of surface pathogens occurs effectively through the initial heating phase. The distinction matters most for poultry and pork.