How many bits does UART 8N1 use per byte?

UART 8N1 sends one start bit, eight data bits, no parity bit, and one stop bit. Each eight-bit payload byte therefore occupies ten bit times on the wire.

What is the real byte rate at 115200 baud with 8N1?

The ideal maximum is 11,520 eight-bit characters per second because each 8N1 character consumes ten bit times. Protocol gaps and software overhead can reduce application throughput.

How is UART baud error calculated?

Baud error is the achieved baud minus the target baud, divided by the target baud, multiplied by 100. Both endpoints contribute to the total timing mismatch.

Frame, throughput, and clock check

UART Baud Rate & 8N1 Throughput Calculator

Convert framing settings into real payload throughput, then check whether a peripheral clock can generate the requested baud rate with enough timing margin.

Tool Published Jul 14, 2026 Generic divider model; verify the MCU reference manual

UART configuration

Values update immediately.

Common baud rates

Baud rate Payload characters Data bits Parity Stop bits Peripheral clock (MHz) Oversampling Divider resolution

Calculated result

115200 8N1

Bits per frame: 10 bits
Payload efficiency: 80.00%
Characters per second: 11,520
Payload bit rate: 92.16 kbit/s
Wire time for payload: 86.806 ms

Clock divider estimate

Ideal divider: 26.041667
Selected divider: 26
Actual baud: 115,384.62
Signed error: +0.160%

Low local divider error. Include the remote endpoint, oscillator tolerance, temperature, and the device sampling rules in the full budget.

This is a generic clock / (oversampling x divider) model, not a register value. UART baud generators use device-specific formulas, rounding, and fractional encodings.

Why 8N1 is ten bits per byte

An 8N1 frame contains one start bit, eight data bits, no parity bit, and one stop bit. At 115200 baud the ideal ceiling is therefore 11,520 eight-bit characters per second, before protocol pauses, buffering, or application processing.

bits_per_frame = 1 + data_bits + parity_bits + stop_bits
characters_per_second = baud / bits_per_frame
wire_time = characters x bits_per_frame / baud

Use baud error as a budget

Divider error is only one contributor. The transmitter and receiver each have clock tolerance, drift, and sampling behavior. Compare the combined worst case with the limit in both devices' reference manuals, especially for longer frames or internal RC clocks.

Calculate the achieved baud on both endpoints.
Add clock-source tolerance and temperature drift.
Check oversampling and permitted mismatch in the datasheets.
Confirm the bit time and stop-bit sample point on a scope or logic analyzer.

Frequently asked questions

Is baud the same as bytes per second?

No. Baud counts symbols per second; conventional UART sends one bit per symbol, but start, parity, and stop bits add framing overhead around the payload.

Does a low calculated divider error guarantee the link?

No. It does not include the other endpoint, oscillator tolerance, electrical distortion, or device-specific sampling limits.

Can I enter a fractional divider?

Choose the nearest resolution offered by the tool, then translate the result using the exact fractional encoding documented for your MCU.