Baud rate and serial throughput calculator
Enter the baud rate and the serial settings, such as 9600 8N1. The calculator gives the bit rate, the bits in each character frame, how many bytes per second really get through, the time of one bit and one character, and the time to send a given number of bytes.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the baud rate. For a UART serial port keep bits per symbol at 1.
- Choose the frame: data bits, parity and stop bits (for example 8, None, 1 for 8N1).
- Enter how many bytes to send to get the transfer time.
- Bit rate = baud × bits per symbol
- Frame = 1 start bit + data bits + parity bit (0 or 1) + stop bits
- Characters per second = bit rate ÷ frame bits
- Efficiency = data bits ÷ frame bits
- Bit time = 1 ÷ bit rate; character time = frame ÷ bit rate
- Transfer time = bytes ÷ characters per second
Worked example
9600 baud, 8N1, sending 1,024 bytes:
- Bit rate: 9,600 bit/s; frame: 1 + 8 + 0 + 1 = 10 bit.
- Characters per second: 9,600 ÷ 10 = 960; efficiency 80 %.
- One bit lasts 104.1667 µs, one character 1.0417 ms.
- 1,024 bytes take 1,024 ÷ 960 = 1.067 s.
Tips
- Budget 10 bits per byte for 8N1 as a quick rule: 115200 baud moves about 11.5 KB per second.
- Clock error adds up over a frame. UART receivers resynchronise on every start bit, so the two clocks only need to agree within a few percent over one frame.
- Protocol overhead is extra. Packet headers, checksums and pauses between frames reduce the real throughput below this figure.
Frequently asked questions
Is baud the same as bits per second?
Only when each symbol carries one bit, which is the case on a UART serial line. Baud counts symbols per second; bit rate = baud × bits per symbol. A modem sending 2400 symbols per second with 16 possible states (4 bits each) carries 9600 bit/s.
How many bytes per second does 9600 baud give?
With 8N1, each byte is sent as 10 bits: 1 start bit, 8 data bits and 1 stop bit. 9600 ÷ 10 = 960 bytes per second, not 1200. With parity (8E1) the frame is 11 bits and you get about 873 bytes per second.
What does 8N1 mean?
8 data bits, no parity, 1 stop bit, the most common serial setting. 7E1 is 7 data bits, even parity and 1 stop bit. Every frame also starts with one start bit, which is never written in the shorthand.
What are the common baud rates?
1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 are the classic ones; many microcontrollers and USB adapters also support 230400, 460800 and higher. Both ends must use the same rate and frame settings.