FFT Bin Resolution Calculator
Bin width, duration, and frequency resolution for an FFT.
How to Use
- Enter sample rate and FFT size N.
- Δf = fs/N. Capture time = N/fs.
Show Work
Formulas
History of FFT Bin Analysis
The FFT\'s bin structure — N output values corresponding to frequencies 0, fs/N, 2fs/N, ... — falls directly out of the Cooley-Tukey algorithm published in 1965. Each bin is the magnitude of the complex coefficient at that specific integer multiple of 1/T where T = N/fs is the window duration. Signals whose frequency doesn\'t land exactly on a bin center "leak" energy into neighboring bins — the famous spectral leakage problem.
Windowing functions (Hann 1946, Hamming 1970, Blackman-Harris 1978, Kaiser 1966) trade main-lobe width for side-lobe suppression to manage leakage. Rectangular (no window) has the narrowest main lobe but worst side lobes (−13 dB first side lobe). Hann gives a good balance (−32 dB side lobes, 1.5× wider main lobe). Blackman-Harris achieves −92 dB side lobes at the cost of 2× main lobe width.
Modern practice: for waveforms known to have content at exactly one bin frequency, no window is needed. For arbitrary signals or spectrum surveys, Hann is the default; Blackman-Harris or Kaiser when side-lobe rejection matters more than main-lobe width. Every DSP library and spectrum-analyzer firmware implements a selection of these, chosen from a menu.
About This Calculator
Enter sample rate and FFT size. The tool returns bin width Δf, capture window duration T, the maximum meaningful frequency (Nyquist = fs/2), and the number of useful bins (N/2 + 1).
Use these numbers for: sizing FFT buffers in firmware, designing oscilloscope FFT display parameters, sizing SDR waterfall displays, and matching FFT resolution to signal requirements (audio ~10 Hz bins, precision measurement ~1 Hz, RF wideband ~1 kHz). All math runs client-side.
About the FFT Bin Resolution Calculator
Use the FFT Bin Resolution Calculator — a free, easy tool for electronics and circuit design. Nothing is uploaded, and you do not need an account. Bin width, duration, and frequency resolution for an FFT.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Why power of 2?
Classic Cooley–Tukey FFT is fastest at N = 2ᵏ.
Leakage?
A sinusoid not on a bin center smears across neighbors — windowing reduces it.
How do I use the FFT Bin Resolution Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Audio Analyzer
48 kHz, 4096 → 11.7 Hz bins.
RF SDR
2 Msps, 65536 → 30.5 Hz bins.
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