Fourier Transform Calculator

What this site does. You bring a table of measurements, it gives you numbers back. This page takes a signal sampled over time and tells you which frequencies it is made of, and how strong each one is. It runs entirely in your browser — nothing is uploaded, nothing is stored. If you want the reasoning rather than the answer, the Fourier transform article walks through the DFT, the FFT and what a spectrum can and cannot show.

Each column is taken as evenly spaced samples, in row order - there is no time column here. If your samples are not evenly spaced, use the advanced calculator, which checks the spacing.

1. Paste your data into the Input grid — straight from a spreadsheet, or as CSV/TSV text — or import a CSV/TSV file. Up to four columns, each one its own signal. Up to 1,024 rows per column.
2. Pick a window: rectangular (none) when every tone completes a whole number of cycles, Hann for everything else.
3. Press transform. Each column gets its own DFT. Until then the spectrum chart stays empty; a paste or an import redraws the input chart at once, and the spectrum changes only on the next press.
4. Read the result. The Output grid lists bin k and one amplitude per column, from bin 0 to the Nyquist bin N/2. A sine of amplitude A reads A. Bin k is k cycles per record - multiply by your sampling rate over N for Hz. Export saves the Output grid as a CSV/TSV file.

Blank cells and text are skipped, so columns may have different lengths; each gets its own N and its own bins.