The　cable　tension　plays　an　important　role　in　the　construction,　assessment　and　long-term　health　monitoring　of　cable　structures.　The　cable　vibration　equation　is　nonlinear　if　cable　sag　and　bending　stiffness　are　included.　The　engineering　implementation　of　a　vibration-based　cable　tension　evaluation　is　mostly　carried　out　by　the　simple　taut　string　theory.　However,　the　simple　theory　may　cause　unacceptable　errors　in　many　applications　since　the　cable　sag　and　bending　stiffness　are　ignored.　From　the　practical　point　of　view,　it　is　necessary　to　have　empirical　formulas　if　they　are　simple　and　yet　accurate.　Based　on　the　solutions　by　means　of　energy　method　and　fitting　the　exact　solutions　of　cable　vibration　equations　where　the　cable　sag　and　bending　stiffness　are　respectively　taken　into　account,　the　empirical　formulas　are　proposed　in　the　paper　to　estimate　cable　tension　based　on　the　cable　fundamental　frequency　only.　The　applicability　of　the　proposed　formulas　is　verified　by　comparing　the　results　with　those　reported　in　the　literatures　and　with　the　experimental　results　carried　out　on　the　stay　cables　in　the　laboratory.　The　proposed　formulas　are　straightforward　and　they　are　convenient　for　practical　engineers　to　fast　estimate　the　cable　tension　by　the　cable　fundamental　frequency.