Calculate chains per hour, distance, or time by selecting a solve mode and entering two required values, converting feet, meters, yards, hours, minutes, or seconds with unit conversions.
Chains Per Hour Formula
The calculator uses the distance-rate-time relationship. It converts distance to feet, time to hours, and rate to chains per hour, with 1 chain = 66 feet.
- CPH = chains per hour
- D = forward spread distance, converted to feet
- T = total time, converted to hours
Select spread rate, spread distance, or elapsed time, then enter the two required values. Zero distance is valid; solving a rate requires positive time and solving time requires a positive rate. The selected units are converted before the formula is applied, then the result is converted back to the unit you selected.
Unit Conversions Used in the Calculation
| Input type | Unit | Conversion to base unit |
|---|---|---|
| Distance | ft | 1 ft = 1 ft |
| Distance | m | 1 m ≈ 3.28084 ft (1 ft = 0.3048 m exactly) |
| Distance | yd | 1 yd = 3 ft |
| Time | minutes | 1 minute = 1/60 hour |
| Time | seconds | 1 second = 1/3600 hour |
Chains Per Hour Rate Conversions
| Rate unit | Equivalent in chains/hour |
|---|---|
| 1 chain/hour | 1 chains/hour |
| 1 chain/min | 60 chains/hour |
| 1 chain/sec | 3600 chains/hour |
Example Calculations
Example 1: Calculate chains per hour
You enter a forward spread distance of 120 ft and a total time of 2 hours.
The result is 0.909091 chains/hour.
Example 2: Calculate time
You enter a forward spread distance of 300 ft and a rate of 75 chains/hour.
The result is 0.060606 hours (about 3.64 minutes).
FAQ
What does chains per hour mean?
Chains per hour measures linear forward spread using 1 chain = 66 feet. This calculator performs distance-rate-time arithmetic with an entered or observed rate; it does not predict fire behavior or establish safe firefighting actions.
Can you use minutes or seconds instead of hours?
Yes. If you select minutes or seconds, the calculator converts the time to hours for the formula. For example, 30 minutes is converted to 0.5 hours before calculating chains per hour.
How do you choose the value to calculate?
Choose a solve mode. Enter the two displayed required values and select Calculate; the result appears below the inputs.
