Heat index calculator
Type the air temperature and the humidity and get the National Weather Service heat index, its caution category, and what the youth soccer bodies that publish heat index limits say to do at that number: water breaks, shorter halves, or stop. U.S. Soccer sets its limits in wet bulb globe temperature, a different reading, so those are shown separately and labeled as WBGT. Every threshold links to the document it came from.
70 to 110 F, the range the NWS chart covers. The shade reading from a thermometer at the field, or the local forecast.
Heat index 100 F, NWS Extreme Caution.
Heat stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or physical activity.
NWS chart values are for shade and light wind. The NWS says full sunshine can raise the heat index by up to 15 F, so on a field in the sun treat this number as a floor.
What the bodies that use heat index say at 100 F
- Massachusetts Youth Soccer · 100 to 104 F
- Games and training: Mandatory two-minute water breaks per half with running time. Each half shortened by ten minutes.
- Indiana Soccer · 100 to 103 F
- Training: Mandatory water breaks every 20 minutes for 10 minutes. Postpone practice to later in the day if possible. Re-check every 30 minutes.
- Games: Mandatory two-minute water breaks halfway through each half. Re-check temperature and humidity every 30 minutes.
- Michigan High School Athletic Association · 100 to 104 F
- Games and training: Mandatory water breaks every 30 minutes for 10 minutes. Alter the uniform, reduce outside time, postpone practice to later in the day. Re-check every 30 minutes.
The math follows the NWS heat index equation page, including its adjustment for humidity above 85% at 80 to 87 F. In that humid corner the NWS chart's printed values match the regression without the adjustment, so the chart reads up to two degrees lower than this calculator; everywhere else the two agree to within a degree. The chart stops at an air temperature of 110 F and a heat index of 137 F, and so does this page: past 137 F it says so instead of printing a number.
Heat index versus WBGT
The heat index is the NWS's measure of "how hot it really feels" once relative humidity is combined with the air temperature, calculated for shade and light wind. The NWS says full sunshine can push it up to 15 F higher.
Wet bulb globe temperature is a different measurement. The NWS describes it as a measure of heat stress in direct sunlight that takes into account temperature, humidity, wind speed, sun angle and cloud cover, and it is read from a WBGT device at the field. U.S. Soccer's Recognize to Recover heat guidelines are written in WBGT, with alert levels that shift by region, and Georgia Soccer's policy is WBGT as well. The NFHS heat position statement points coaches to WBGT readings and asks for lower intensity and more rest breaks as conditions get hotter and more humid, without naming a number.
This calculator gives a heat index only. It cannot be looked up in a WBGT table. Georgia Soccer offers the one bridge on this page, that a WBGT of 92 is "somewhat comparable" to a heat index of 104 to 105, and the page repeats it in those words rather than converting.
The NWS caution categories
| Category | Heat index | Effect on the body, as the NWS puts it |
|---|---|---|
| Caution | 80 to 90 F | Fatigue possible with prolonged exposure and/or physical activity. |
| Extreme Caution | 90 to 103 F | Heat stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or physical activity. |
| Danger | 103 to 124 F | Heat cramps or heat exhaustion likely, and heat stroke possible with prolonged exposure and/or physical activity. |
| Extreme Danger | 125 F or higher | Heat stroke highly likely. |
The NWS prints the ranges with shared endpoints. This page puts a value on a shared endpoint in the higher category, so 90 F is Extreme Caution and 103 F is Danger. National Weather Service, Amarillo: Heat Index: classifications and effects on the body
Play modifications by heat index
The three bodies below publish their limits in heat index. Each table is one document's own ranges and wording, condensed but not changed. Where a document says "under 90" or "above 104" the neighboring rows meet on whole degrees.
Massachusetts Youth Soccer
| Heat index | Applies to | What the document says |
|---|---|---|
| up to 84 F | Games and training | Normal play. |
| 85 to 89 F | Games and training | Mandatory two-minute water breaks per half with running time. |
| 90 to 99 F | Games and training | Mandatory two-minute water breaks per half with running time. Each half shortened by five minutes. |
| 100 to 104 F | Games and training | Mandatory two-minute water breaks per half with running time. Each half shortened by ten minutes. |
| 105 F and above | Games and training | Suspend play. |
Indiana Soccer
| Heat index | Applies to | What the document says |
|---|---|---|
| up to 89 F | Training | Water always available. Optional water breaks every 30 minutes for 10 minutes. Ice-down towels for cooling. |
| up to 89 F | Games | Water always available. |
| 90 to 94 F | Training | Recommended water breaks every 30 minutes for 10 minutes. Ice-down towels, sprinklers, fans or shade for cooling. |
| 90 to 94 F | Games | Recommended two-minute water breaks halfway through each half, when the ball is out of play. |
| 95 to 99 F | Training | Mandatory water breaks every 30 minutes for 10 minutes. Re-check temperature and humidity every 30 minutes. |
| 95 to 99 F | Games | Mandatory two-minute water breaks halfway through each half. Re-check temperature and humidity every 30 minutes. |
| 100 to 103 F | Training | Mandatory water breaks every 20 minutes for 10 minutes. Postpone practice to later in the day if possible. Re-check every 30 minutes. |
| 100 to 103 F | Games | Mandatory two-minute water breaks halfway through each half. Re-check temperature and humidity every 30 minutes. |
| 104 F and above | Games and training | Stop all outside activity in practice and play, and all inside activity if air conditioning is unavailable. |
Michigan High School Athletic Association
| Heat index | Applies to | What the document says |
|---|---|---|
| up to 94 F | Games and training | Water always available. Optional water breaks every 30 minutes for 10 minutes. Ice-down towels for cooling. |
| 95 to 99 F | Games and training | Optional water breaks every 30 minutes for 10 minutes. Reduce time of outside activity and consider postponing practice to later in the day. Re-check every 30 minutes. |
| 100 to 104 F | Games and training | Mandatory water breaks every 30 minutes for 10 minutes. Alter the uniform, reduce outside time, postpone practice to later in the day. Re-check every 30 minutes. |
| 105 F and above | Games and training | Stop all outside activity in practice and play, and all inside activity if air conditioning is unavailable. |
WBGT limits (not heat index)
U.S. Soccer's alert levels, in wet bulb globe temperature. The region category comes from a map in the guidelines that this page does not reproduce, so all three columns are shown. A heat index from the calculator above cannot be read against these numbers.
| Alert level | WBGT, region 1 | Region 2 | Region 3 | Conditions | Training |
|---|---|---|---|---|---|
| Green | under 76.1 F | under 79.8 F | under 82.1 F | Good conditions | Normal activities. Three separate 3-minute breaks each hour of training, or a 10-minute break every 40 minutes. |
| Yellow | 76.3 to 81.0 F | 79.9 to 84.6 F | 82.2 to 87.0 F | Less than ideal conditions | Use discretion. Three separate 4-minute breaks each hour, or a 12-minute break every 40 minutes of training. |
| Orange | 81.1 to 84.1 F | 84.7 to 87.7 F | 87.1 to 90.0 F | Moderate risk for heat related illness | Maximum of 2 hours of training with four separate 4-minute breaks each hour, or a 10-minute break every 30 minutes of training. |
| Red | 84.2 to 86.1 F | 87.8 to 89.7 F | 90.1 to 91.9 F | High risk for heat related illness | Maximum of 1 hour of training with four separate 4-minute breaks within the hour. No additional conditioning allowed. |
| Black | over 86.2 F | over 89.8 F | over 92.0 F | Extreme conditions | No outdoor training. Delay training until cooler, or cancel training. |
Match play and cancellation, in WBGT
| Body | WBGT | Applies to | What the document says |
|---|---|---|---|
| U.S. Soccer | 89.6 F and above | Games | Scheduled hydration breaks of four minutes for each 30 minutes of continuous play; in a 90-minute match, at minute 30 and minute 75. |
| U.S. Soccer | over 86.2 F (region category 1), over 89.9 F (category 2), over 92.0 F (category 3) | Games and training | Training or match play canceled or delayed until cooler. |
| Georgia Soccer | 92 F and above | Training | Training and practice suspended until it is cooler. |
| Georgia Soccer | 92 F and above | Games | Water breaks of four minutes for every 30 minutes of play. If conditions are hotter, or the game is on artificial turf, two water breaks per half may be necessary. |
The guidelines print category 2 as 89.8 in the alert level table and 89.9 in the cancellation text; both are shown as printed.
Georgia Soccer adds that a WBGT reading of 92 is "somewhat comparable" to a heat index of 104 to 105. Georgia Soccer: Heat Policy
Questions
- What heat index is too hot for youth soccer?
- There is no single national number. The bodies that publish limits in heat index stop at about the same place: Massachusetts Youth Soccer suspends play at 105 F, Indiana Soccer stops all outside activity at 104 F and above, and the Michigan High School Athletic Association's model policy stops all outside activity above 104 F. U.S. Soccer and Georgia Soccer set their limits in wet bulb globe temperature instead, which this calculator does not measure. The National Weather Service calls a heat index of 103 to 124 F Danger. Your league's own policy governs.
- Is the heat index the same as WBGT?
- No. The NWS heat index combines air temperature and relative humidity and is calculated for shade. Wet bulb globe temperature is, in the NWS's words, a measure of heat stress in direct sunlight that also takes in wind speed, sun angle and cloud cover. U.S. Soccer's Recognize to Recover heat guidelines set their alert levels in WBGT by region, and Georgia Soccer says a WBGT of 92 is somewhat comparable to a heat index of 104 to 105 but does not turn one into the other. Neither does this page.
- When should a youth soccer game add water breaks?
- Massachusetts Youth Soccer makes two-minute water breaks per half mandatory from a heat index of 85 F. Indiana Soccer recommends a two-minute break halfway through each half at 90 to 94 F and makes it mandatory from 95 F. The MHSAA model policy makes ten-minute breaks every 30 minutes mandatory above 99 F. U.S. Soccer schedules four-minute hydration breaks for every 30 minutes of play once the WBGT reaches 89.6 F, which in a 90-minute match means minute 30 and minute 75.
- Does the heat index account for the sun?
- No. NWS heat index values are for shady, light wind conditions, and the NWS says full sunshine can raise the heat index by up to 15 F. On a field in full sun, treat the number as a floor. Going the other way, the MHSAA policy notes that below 80 F there is no combination of heat and humidity that calls for curtailing activity.
Sources
Every figure on this page was read from one of these documents on September 5, 2026. The bodies revise them; if your league's policy says otherwise, the league is right.
- The Heat Index Equation · National Weather Service, Weather Prediction Center
- Heat Index chart and explanation · National Weather Service
- Heat Index: classifications and effects on the body · National Weather Service, Amarillo
- WetBulb Globe Temperature · National Weather Service, Tulsa
- Heat Guidelines (Recognize to Recover) · U.S. Soccer, with the Korey Stringer Institute
- Environmental Conditions, Recognize to Recover · U.S. Soccer
- Heat Acclimatization and Heat Illness Prevention Position Statement (April 2022) · NFHS Sports Medicine Advisory Committee
- Heat Policy · Georgia Soccer
- Safe Soccer: hot weather · Massachusetts Youth Soccer
- Hot Weather Recommendations · Indiana Soccer
- Model Policy for Managing Heat and Humidity (adopted March 22, 2013) · Michigan High School Athletic Association
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