What is FFT frequency resolution?

Frequency resolution (Δf) is the spacing between adjacent frequency bins in an FFT output. It equals the sample rate divided by the FFT size: Δf = fs / N. A smaller Δf means you can distinguish frequencies that are closer together.

How does FFT size affect frequency resolution?

Doubling the FFT size halves Δf, giving finer frequency resolution. The trade-off is that a larger FFT requires a proportionally longer time window (T = N / fs), so the analysis covers more time and temporal detail is reduced.

What is the Nyquist frequency?

The Nyquist frequency is fs / 2 — the highest frequency an FFT can represent without aliasing. For a 44100 Hz sample rate the Nyquist limit is 22050 Hz. Bins above this index are mirror images and not used.

How many usable frequency bins does an FFT produce?

A real-valued FFT of size N yields N/2 + 1 unique bins: bin 0 (DC) through bin N/2 (Nyquist). The remaining N/2 − 1 bins are complex conjugates and carry no new information.

Why must the FFT size be a power of 2?

The Cooley-Tukey FFT algorithm divides the transform recursively in half, requiring N to be a power of 2 for maximum efficiency. Non-power-of-2 sizes require mixed-radix FFTs or zero-padding, which is why hardware and software libraries almost always use power-of-2 sizes.

What does bin 0 represent?

Bin 0 is the DC component — the average value of the signal over the analysis window. Its center frequency is 0 Hz. Bin 1 has center frequency Δf, bin 2 has 2 × Δf, and so on up to bin N/2 at the Nyquist frequency.

FFT Frequency Resolution Calculator

Name: FFT Frequency Resolution Calculator
Availability: InStock
Author: Nham Vu

Enter a sample rate and FFT size to compute Δf, time resolution, bin count, Nyquist frequency, and a bin-frequency table.

Parameters

Sample Rate (fs)

FFT Size (N)

Formulas

Δf = fs / N

T = N / fs

Bins = N/2 + 1

Nyquist = fs / 2

Results

Frequency Resolution (Δf)

fs / N

—

Time Resolution (T)

N / fs

—

Frequency Bins

N/2 + 1

—

bins

Nyquist Frequency

fs / 2

—

Bin Spacing

center freq of bin k = k × Δf

—

Hz / bin

Bin Center Frequencies

Center frequency of bin k = k × Δf. Bin 0 is DC (0 Hz); bin N/2 is the Nyquist limit.

Bin (k)	Center Frequency	Note
Click Calculate to populate the table.

Showing bins 0–10 plus the Nyquist bin (N/2).

Summary

Enter a sample rate and FFT size to compute Δf, time resolution, bin count, Nyquist frequency, and a bin-frequency table.

How it works

Enter the sample rate (fs) in Hz — for example 44100 for CD-quality audio.
Select the FFT size (N) from the dropdown of standard powers of 2 (64 through 16384).
Click Calculate. The tool applies Δf = fs / N and derives all secondary values from that ratio.
The bin table lists the center frequency of each bin: bin k has center frequency k × Δf.
Adjust N to see how doubling the FFT size halves Δf and doubles the time window.

Use cases

Choose an FFT size for a spectrum analyzer to achieve a target frequency resolution.
Calculate the time window length required to resolve two close spectral peaks.
Determine how many usable frequency bins a given FFT produces before the Nyquist limit.
Verify that the lowest frequency of interest falls within a single FFT bin at a chosen N.
Compare trade-offs between time and frequency resolution when designing a filterbank.
Set up STFT parameters in audio or vibration analysis pipelines.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu