UART Transmission Time Calculator
Estimate how long an asynchronous serial transfer occupies the wire, including start, parity, and stop-bit overhead.
Estimated result
- Bits per frame
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- Total transmitted bits
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- Transmission time
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- Payload throughput
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Formula
time = total bits ÷ baud rate
Formula and assumptions
One start bit is added to the selected data bits, an optional parity bit, and the selected stop-bit duration. Bits per frame = 1 + data bits + parity bit + stop bits. Total bits = frame bits × number of bytes. Transmission time = total bits ÷ baud rate. The throughput result treats each entered byte as eight useful payload bits.
Worked example
At 115,200 baud, 100 bytes in 8-N-1 framing use 10 bits per frame and 1,000 line bits. The transfer takes about 8.681 ms, while useful payload throughput is 92,160 bit/s.
How to use this calculator
- Enter values using the units shown beside each field.
- Choose the framing or hardware options that match your design.
- Select Calculate, then compare the result with your timing or bandwidth budget.
- Check the assumptions and your component reference manual before committing a design.
Common mistakes
- Counting only eight data bits and ignoring framing overhead.
- Confusing baud rate with bytes per second.
- Assuming software latency, buffering, or flow control is included in wire time.
- Selecting a frame format that the remote endpoint does not support.
Frequently asked questions
Does baud rate equal payload bit rate?
No. Start, parity, and stop bits consume line time, so payload throughput is lower than the baud rate.
Why is one start bit assumed?
Conventional asynchronous UART frames use one start bit. This calculator models that common format.
Can a UART use 1.5 stop bits?
Some UART modes support it. Confirm support in both endpoints before using that selection.