Understand the relationship
The reasoning behind the result
An encounter rate has a distance denominator
When only count and walked distance are known, count per kilometre is a descriptive encounter rate. Doubling survey length doubles the exposure denominator. Pooling total counts over total distance respects unequal lengths.
Without a defined surveyed area or a fitted detection model, encounters per kilometre cannot be converted into individuals per hectare. The line mode therefore supplies no area-density claim.
A strip survey adds a geometric assumption
Astrip = length × full width
The full width includes both sides of the centre line if both were surveyed. For a strip extending 2 m to each side, enter 4 m. Each transect's area is calculated separately before areas are added.
Strip density here is observed count per surveyed area. It assumes the rectangular area description is appropriate and avoids overlapping area. Perfect detection would be an additional condition for interpreting it as true population density.
This is not distance-sampling inference
Distance sampling uses detection distances and a statistical detection function to estimate effective area and abundance. Merely entering a strip width does not fit that model.
Moving organisms, repeat encounters, habitat differences and unequal observation conditions can change the meaning of the count. Retain survey protocol and counting-unit definitions alongside the numerical result.
Follow the numbers
Two full-width strips
- A 100 m transect with full width 4 m covers 400 m² and records 12 individuals.
- A 200 m transect with the same full width covers 800 m² and records eight.
- Pooled observed density = 20/1,200 = 0.0166667/m², or 166.667/ha.
The larger transect contributes more sampled area. The pooled result does not average their two densities equally.
Quick guide
How to use this calculator
- Choose a distance-only encounter record or a fixed-width strip survey.
- Enter count and length for every transect; strip mode also needs its full surveyed width.
- Read the pooled denominator and individual transect results.
- Do not interpret an encounter rate as area density or an observed strip density as detection-corrected abundance.
Calculation method
Calculation and interpretation
Match the denominator to the survey design: distance travelled or area observed.
Encounter rate = Σcount/(Σlength/1000); strip density = Σcount/Σ(length × full width)
Worked example
Two full-width strips
The larger transect contributes more sampled area. The pooled result does not average their two densities equally.
Encounter rate = Σcount/(Σlength/1000); strip density = Σcount/Σ(length × full width)
Supported inputs
Precision and limits
Sampling assumptions remain visible
These calculations summarize entered observations under the stated sampling model. They do not establish representative sampling, independent observations, perfect detection, habitat suitability or a population-management decision.
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