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 |
| Oct 30, 4:00 PM EDT | 90 SFU |
| Oct 29, 4:00 PM EDT | 89 SFU |
| Oct 28, 4:00 PM EDT | 93 SFU |
| Oct 27, 4:00 PM EDT | 89 SFU |
| Oct 26, 4:00 PM EDT | 91 SFU |
| Oct 25, 4:00 PM EDT | 89 SFU |
| Oct 24, 4:00 PM EDT | 93 SFU |
| Oct 23, 4:00 PM EDT | 101 SFU |
| Oct 22, 4:00 PM EDT | 106 SFU |
| Oct 21, 4:00 PM EDT | 115 SFU |
| Oct 20, 4:00 PM EDT | 121 SFU |
| Oct 19, 4:00 PM EDT | 121 SFU |
| Oct 18, 4:00 PM EDT | 137 SFU |
| Oct 17, 4:00 PM EDT | 132 SFU |
| Oct 16, 4:00 PM EDT | 131 SFU |
| Oct 15, 4:00 PM EDT | 126 SFU |
| Oct 14, 4:00 PM EDT | 123 SFU |
| Oct 13, 4:00 PM EDT | 136 SFU |
| Oct 12, 4:00 PM EDT | 123 SFU |
| Oct 11, 4:00 PM EDT | 122 SFU |
| Oct 10, 4:00 PM EDT | 126 SFU |
| Oct 9, 4:00 PM EDT | 121 SFU |
| Oct 8, 4:00 PM EDT | 119 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.