CAN Bus Load Calculator
Plan Classical CAN capacity with transparent 11-bit and 29-bit identifier estimates. Compare a baseline with a deliberately conservative stuffing allowance.
Estimated result
- Unstuffed frame length
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- Conservative frame length
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- Frame time, unstuffed
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- Frame time, conservative
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- Bus load, unstuffed
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- Bus load, conservative
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- Remaining capacity
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Formula and assumptions
The baseline uses 47 bits for a standard data frame or 67 bits for an extended data frame, including the three-bit intermission, then adds 8 bits per payload byte. Load (%) = frame bits × messages/s × message count ÷ bit rate × 100. The conservative result multiplies frame length by 1.20 and rounds up. This is a planning allowance, not an exact bit-stuffing simulation.
Worked example
A standard 8-byte frame is estimated at 111 unstuffed bits. At 500 kbit/s and 1,000 frames/s, it occupies about 22.2% of the bus; the conservative 134-bit estimate occupies about 26.8%.
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
- Treating the stuffing allowance as an exact worst-case frame encoding.
- Ignoring higher-priority traffic, retransmissions, error frames, or diagnostic bursts.
- Using an average load that leaves no margin for latency-sensitive traffic.
- Applying Classical CAN arithmetic to CAN FD frames.
Frequently asked questions
Is the result exact?
No. Arbitration, error frames, retransmission, oscillator tolerance, and the actual stuffing pattern can change observed utilization.
Why provide two estimates?
The unstuffed value is a baseline; the conservative value adds 20 percent to represent a planning allowance for stuffing.
Does this calculator support CAN FD?
No. Version one models Classical CAN with data lengths from zero to eight bytes.