Calculate frequency bandwidth
Enter lower and upper cutoff frequencies in hertz, with the upper value greater than the lower value.
About frequency bandwidth
Frequency bandwidth is the span between the upper and lower limits of a frequency range. This calculator subtracts the lower frequency from the upper frequency to obtain absolute bandwidth in hertz. It also reports the arithmetic center frequency, quality factor, and fractional bandwidth. These related quantities help describe filters, resonators, communication channels, sensors, amplifiers, and any system whose useful response occupies a defined frequency interval.
The arithmetic center frequency is the sum of the two edge frequencies divided by two. Quality factor, often written Q, is center frequency divided by bandwidth. A high Q describes a narrow range relative to its center, while a low Q describes a broader range. Fractional bandwidth is bandwidth divided by center frequency and is displayed here as a percentage. For example, an 80 MHz channel centered at 2.44 GHz has a fractional bandwidth of about 3.28 percent and a Q of 30.5.
Before entering limits, determine what the edges represent. Filter specifications often use half-power or minus-three-decibel cutoff points, but other systems may define occupied bandwidth, emission masks, usable response, or measurement thresholds differently. Results are meaningful only when both limits use the same definition and units. Convert kilohertz, megahertz, or gigahertz to hertz before entry. The upper frequency must exceed the lower frequency so bandwidth is positive and Q remains defined.
Arithmetic center frequency is appropriate for the formulas on this page and many linear-bandwidth summaries. Some filter and logarithmic-frequency designs instead use the geometric mean of the cutoff frequencies as a resonant or logarithmic center. For narrow bands the two centers are close, but they can differ noticeably for wide ratios. Check the convention required by your discipline before applying the result. Fractional bandwidth below roughly ten percent is commonly described as narrowband, though the exact threshold depends on context. Real frequency response is rarely rectangular, so ripple, roll-off, group delay, noise, and adjacent-channel requirements may matter alongside the four calculated values. Use measured or simulated cutoff points for detailed engineering decisions.
Frequently asked questions
How is frequency bandwidth calculated?
Subtract the lower frequency from the upper frequency. Both edge values must use the same unit and measurement criterion.
What does a high Q factor mean?
A high Q means bandwidth is narrow relative to center frequency. It often indicates greater selectivity in a resonator or band-pass filter.
What is fractional bandwidth?
Fractional bandwidth is absolute bandwidth divided by center frequency. Expressing it as a percentage makes differently scaled frequency ranges easier to compare.
Is center frequency always the arithmetic mean?
This calculator uses the arithmetic mean required by its stated formulas. Some logarithmic or resonant designs use the geometric mean instead, so check the applicable convention.
What counts as narrowband?
A fractional bandwidth below about ten percent is a common engineering rule of thumb. The practical definition depends on the application, standard, and approximations being used.