The buffer determines how long an audio interface or DAW collects samples before processing them. The calculator converts buffer size and sample rate into milliseconds, adds the extra delays for input and output, estimates the path from input to output and shows how far sound travels in the same time.
The two lower fields take additional delays for converters and safety buffers, as far as the driver or the DAW shows them; without such values both stay at 0.
The highlighted row is the current buffer size. At 44.1 kHz, 441 and 880 samples correspond to the 10 and roughly 20 ms named in the FL Studio manual.
Both fields use the sample rate above, for example for a delay compensation given in samples.
Latency in ms = samples ÷ sample rate × 1000. 441 samples at 44.1 kHz give 10 ms, 512 samples 11.61 ms.
Round trip = input buffer + output buffer + both extra latencies. The calculator assumes the same buffer size for input and output.
Sound travel = latency × speed of sound; at 20 °C sound covers about 344 m per second in air, 0.344 m per millisecond.
Everything is calculated in the browser. Actual latency also depends on the driver, the converters and plugins with look-ahead; a loopback measurement with the audio interface shows the real value. According to the FL Studio manual, the delay between playing and hearing is at least equal to the buffer setting.