What does this number mean?
The Solar Flux Index measures radio energy from the Sun at a wavelength of 10.7 cm. It is reported in solar flux units (SFU) and tracks broad solar activity. One daily value is not a direct measure of an HF path.
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Solar Flux Index (SFI) & F10.7 History
The Solar Flux Index, also called SFI or F10.7, measures solar radio emission at 10.7 centimeters. Explore daily NOAA readings and learn how the trend helps put HF band conditions in context.NOAA observed readings
Solar Flux Index
Latest graphed reading: 125 SFU on Nov 6, 2026, 3:00 PM EST.
NOAA reading 7-day average
View readings as a table
| Date and time (Eastern) | Solar Flux Index |
|---|---|
| Nov 6, 3:00 PM EST | 125 SFU |
| Nov 5, 3:00 PM EST | 124 SFU |
| Nov 4, 3:00 PM EST | 111 SFU |
| Nov 3, 3:00 PM EST | 100 SFU |
| Nov 2, 3:00 PM EST | 97 SFU |
| Nov 1, 3:00 PM EST | 95 SFU |
| Oct 31, 4:00 PM EDT | 92 SFU |
Readings: NOAA 30-day solar flux product. Times are shown in Eastern time. Missing measurements are left blank, not treated as zero. The optional 7-day average is calculated here from consecutive readings.
Why does it matter for HF?
Over days and weeks, stronger solar activity often supports ionization that can help higher HF bands open. Solar flux is useful context alongside sunspots, daylight, season, and geomagnetic conditions.
How should I use the graph?
Look at the direction of the daily readings and optional 7-day average. A rising trend can be encouraging for upper HF, but check current Kp, solar wind, and X-rays before planning a contact.
Learn more from NOAA Space Weather Prediction Center and ARRL's HF propagation guide.