Trout Weight Calculator
Estimate the weight of a trout from its length and girth so you can measure it, log it and let it go.
Open tool : Trout Weight CalculatorTrout Water Temperature Guide
Read water temperature and know when trout feed, when they slow down and when to leave them alone.
Enter a temperature to see the commonly published guidance for that range.
Commonly published temperature ranges
These bands reflect guidance published widely by state fisheries agencies, cold water conservation groups and fly shops. They are educational context, not a regulation and not a threshold specific to your water.
| Range | Band | What is generally reported |
|---|---|---|
| Below 40°F / 4°C | Cold | Trout are slow and hold deep. Feeding windows are short and usually midday. |
| 40 to 50°F / 4 to 10°C | Cool | Activity picks up as the day warms. Midges and early season baetis are the usual food. |
| 50 to 65°F / 10 to 18°C | Prime | The range trout are most commonly reported feeding actively across. Most hatches happen here. |
| 65 to 68°F / 18 to 20°C | Caution | Warm. Dissolved oxygen drops as trout need more of it. Many agencies advise fishing early and cutting the day short. |
| Above 68°F / 20°C | Stop | Widely published as the point at which agencies and conservation groups ask anglers to stop targeting trout. Some waters carry formal restrictions. |
Why the number matters
Trout are cold water fish and cannot regulate their own body temperature. As water warms it holds less dissolved oxygen, and at the same time a trout's demand for oxygen goes up. Being hooked, played and handled on top of that is what does the damage.
That is the whole reason anglers carry a thermometer. It costs a few dollars and it tells you something no forecast can: whether the fish in front of you can take being caught today.
Check your state or provincial agency before you go. Many publish seasonal restrictions, and some rivers run morning only rules through the hottest weeks of summer. Those local numbers and closures override anything on this page.
Common questions
Why does water temperature matter so much
Trout are cold water fish and cannot regulate their own body temperature. Warmer water holds less dissolved oxygen while the fish need more of it, so warm water compounds the stress of being caught and handled.
When should I stop fishing for trout
Many state agencies and conservation groups publish a temperature at which they ask anglers to stop, and some waters get formal restrictions such as morning only hoot owl rules. Those local numbers and rules are the ones to follow. This guide points you at the ranges commonly published so you know to go and check.
Where and when should I take a reading
Take it in the main current rather than a warm shallow edge, and remember water is usually coldest early and warms through the afternoon. A reading at seven in the morning tells you very little about three in the afternoon.