Fish fillets cook fast, and that speed is exactly what makes them easy to overcook. A minute too long turns a moist fillet dry, while a minute too short leaves the centre raw. This free calculator gives you the right time for fish fillets: enter the thickness, pick your method, and it shows the cooking time and the safe internal temperature.
The rule behind the calculator is simple: about 10 minutes of baking for every 25 millimetres of thickness, with pan-frying a little faster and grilling in between. Thickness, not weight, decides the time, because heat travels from the outside in. Two fillets of the same weight can need very different times if one is thick and the other is thin and wide, so measuring thickness with a ruler beats guessing from the packet.
Thickness is the only measurement that matters for a fillet: a 25 millimetre fillet and a 12 millimetre fillet need very different times, even from the same fish. Measure at the thickest point of the fillet, not at the thin tail end. If one end is much thinner, fold it under or remove the fillet a little early, because the thin end will always cook first. Even thickness is the secret to even cooking, and it matters more than any fancy pan or oven setting.
Method changes the time. Baking is gentle and even, and it suits thicker fillets that need time for heat to reach the centre. Pan-frying is faster and gives a crisp crust, but it needs attention and a hot pan. Grilling sits in between, with strong heat from above or below and a short cooking time that suits thinner fillets best.
Watch for the signs of doneness as well as the clock. Fish is ready when it flakes easily with a fork and the flesh turns opaque all the way through. The centre should reach 60 C for safety and the best texture. If the fish still looks shiny and translucent in the middle, give it one more minute and check again, rather than guessing.
Do not move the fish too much while it cooks. In a pan, let the fillet sit still until the underside is golden, then flip it once. Moving it breaks the crust and can tear the flesh. In the oven, use a tray lined with baking paper so the fillet lifts off cleanly, and rest it for one minute before serving so the juices settle.
Season simply and late if you use a marinade with acid. Salt and lemon juice are classic with fish, but a long soak in lemon can start to cook the surface before the heat does. Season just before cooking for a clean flavour, add a squeeze of lemon at the end, and serve at once, because fish cools fast and tastes best hot from the pan or oven.
Save this page for your next fish dinner. The calculator is free, needs no account, and works in your browser on a phone or a computer. Measure the thickness, pick your method, and cook fish with confidence instead of cutting into it to check.
Buying good fish makes the cooking easier. Fresh fillets smell like the sea, not strongly fishy, and the flesh springs back when you press it gently. The skin, if it is still on, should look shiny and tight, and the fillet should sit flat rather than curling at the edges. Buy fish on the day you plan to cook it, keep it cold in the fridge in its wrapper, and take it out ten minutes before cooking so it cooks evenly from edge to centre.