[[Image:pmeter-t.jpg|thumb|right|238px|Et S-meter på en Ten-Tec Orion amatørradio transceiver.]]
Et '''S-meter''' (fra engelsk ''signal strength meter'',<ref>[https://encyclopedia2.thefreedictionary.com/S+meter encyclopedia2.thefreedictionary.com: S meter], [https://web.archive.org/web/20210414013655/https://encyclopedia2.thefreedictionary.com/S+meter backup]</ref> dansk '''signalstyrke-meter''') er en indikator som ofte er på [[kommunikationsmodtager]]e, såsom [[amatørradiomodtager]]e eller [[kortbølgemodtager]]e.  Skalamarkeringerne er afledt fra det subjektive system til at reportere [[signalstyrke]]r fra S1 til S9 som en del af [[RST-kode]]n. Termen '''S-enhed''' kan anvendes til at referere til, hvor meget signalstyrkeændring, der skal til for at flytte en S-meter indikation fra en markering til den næste.<ref>[https://www.rfcafe.com/references/popular-electronics/electrical-units-confusion-popular-electronics-april-1966.htm rfcafe.com: April 1966 Popular Electronics: Confused About S-Units?] Citat: "...Each S−level step indicated a signal decrease of 5 to 6 dB below the previous S−level, again depending on the manufacturer's preference. As you might expect, confusion ensued. Nowadays there is an unofficial but generally adopted definition of S9 through S1, beginning at -73 dBm for S9, and then a 6−dB step size down to S1 level of (8 x −6 dB = −48 dB) = −121 dBm. It applies across the specified receive band(s), independent of frequency. Author Marshall Lincoln reviews S-units and S-meter circuits...An important variable which causes S-meter reports to be inconsistent is the fact that receiver manufacturers do not have a common calibration standard. Also, each manufacturer has his own calibration method...", [https://web.archive.org/web/20210411160005/https://rfcafe.com/references/popular-electronics/electrical-units-confusion-popular-electronics-april-1966.htm backup]</ref>
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