About

Misconfigured serial parameters cause silent data corruption. A single wrong stop bit setting or mismatched baud rate between transmitter and receiver produces garbled output with no error indication. This calculator computes the actual data throughput from your physical baud rate (S) by accounting for protocol overhead: start bits, parity bits, and stop bits that consume bandwidth but carry zero payload. It derives frame efficiency, character rate, and file transfer time for standard UART/RS-232 configurations. The formulas assume asynchronous serial framing per EIA/TIA-232 and ITU-T V.28 standards. Results approximate ideal conditions. Real links degrade further due to clock drift (typically ±2% tolerance), cable capacitance, and noise-induced retransmissions.

Formulas

The total bits per serial frame (F) includes protocol overhead around the payload data bits:

F = B_start + B_data + B_parity + B_stop

For modulated links, the effective bit rate depends on the modulation order M:

R_bit = S × log₂(M)

Actual payload throughput strips out protocol bits:

T = B_dataF × R_bit

Frame efficiency quantifies protocol overhead cost:

η = B_dataF × 100%

Transfer time for a given file size:

t = FileSizeT

Where: S = symbol (baud) rate in Bd, M = modulation states (binary NRZ: M = 2), B_start = start bits (always 1), B_data = data bits (5 - 9), B_parity = parity bit (0 or 1), B_stop = stop bits (1, 1.5, or 2), R_bit = gross bit rate in bps, T = payload throughput in bps, η = frame efficiency.

Reference Data

Baud Rate Bd	Bit Rate (8N1) bps	Throughput (8N1) B/s	Typical Application	Max Cable Length m
300	300	30	Legacy modems, teletype	1500
1200	1200	120	Early modems, MIDI	900
2400	2400	240	GPS receivers (NMEA)	800
4800	4800	480	Industrial sensors, PLC	600
9600	9600	960	Default serial console, Arduino	300
14400	14400	1440	V.32bis modems	250
19200	19200	1920	Industrial automation	200
28800	28800	2880	V.34 modems	150
38400	38400	3840	Medical devices, SCADA	120
57600	57600	5760	GPS high-speed, Bluetooth SPP	100
115200	115200	11520	Embedded debug, Linux console	60
230400	230400	23040	High-speed microcontrollers	30
460800	460800	46080	FTDI USB-serial bridges	15
921600	921600	92160	ESP32, high-speed logging	10
1000000	1000000	100000	Dynamixel servos, USB-UART	8
1500000	1500000	150000	STM32 DMA serial	5
2000000	2000000	200000	CP2102N USB bridge max	3
3000000	3000000	300000	FTDI FT232H max	2

Frequently Asked Questions

Baud rate (S) measures symbols per second on the physical medium. Bit rate (R_bit) measures information bits per second. For binary encoding (NRZ), they are equal: 1 symbol carries 1 bit. With higher-order modulation like QAM-16, each symbol encodes log₂(16) = 4 bits, so a 2400 Bd modem achieves 9600 bps.

In an 8N1 frame (8 data, no parity, 1 stop), the frame is 10 bits with 80% efficiency. Switching to 8E1 (even parity) adds 1 bit, making it 11 bits per frame. Efficiency drops to 72.7%. At 115200 Bd, throughput falls from 11520 to 10473 B/s - a 9.1% penalty for single-bit error detection with no correction capability.

UART receivers sample each bit at the center of its time slot, synchronized from the start bit falling edge. A baud rate mismatch causes the sampling clock to drift. At ±3% error, the last data bit in an 8-bit frame is sampled 24% off-center, producing random framing errors. Most UART hardware tolerates ±2% maximum clock deviation. Crystal oscillators provide <0.01% accuracy; internal RC oscillators may drift 1 - 5% with temperature.

Stop bits define minimum idle time between frames. 1 stop bit is standard for modern hardware. 2 stop bits provide extra recovery time for slow receivers (mechanical teletypes required this). 1.5 stop bits exist for 5-bit Baudot code compatibility. Using 2 stop bits at 9600 Bd with 8N2 config reduces throughput to 873 B/s versus 960 B/s with 8N1 - a 9% reduction.

RS-232 specifies a maximum capacitive load of 2500 pF. Standard cable has approximately 40 - 50 pF/m, giving roughly 15 m at the maximum signaling rate. At lower baud rates, rise time requirements relax, permitting longer cables. RS-422 and RS-485 use differential signaling, achieving 1200 m at 100 kbps. The rule of thumb: baud rate × cable length < 10⁸ for reliable RS-232.

Standard UART uses binary NRZ encoding where 1 symbol = 1 bit, so baud rate equals bit rate. However, dial-up modems use multi-level modulation: a V.34 modem at 3429 Bd with QAM-1664 encoding achieves 33600 bps because each symbol carries up to 9.8 bits. This calculator supports both scenarios via the modulation selector.