Calculator
Example data table
These sample readings show how rates change with surface condition and compaction.
| Scenario | Area method | Runs | Depth drops (mm) | Durations (min) | Avg rate (mm/hr) |
|---|---|---|---|---|---|
| Raised bed, mulched | Ring 20 cm | 3 | 14, 12, 11 | 10, 10, 10 | 74.00 |
| Vegetable row, bare soil | Ring 20 cm | 3 | 10, 9, 8 | 10, 10, 10 | 54.00 |
| Lawn with foot traffic | Ring 20 cm | 2 | 4, 3 | 10, 10 | 21.00 |
| Compacted path edge | Ring 20 cm | 2 | 2, 2 | 10, 10 | 12.00 |
Formula used
- Test area (ring): A = π × (d/2)²
- Depth infiltrated (per run): D is the water level drop (mm)
- Measured infiltration rate (per run): IR = D / (t/60) (mm/hr)
- Infiltrated volume (per run): V = A × (D/1000) (m³)
- Average measured rate: mean of run rates
- Adjusted rate (optional): IR_adj = IR_avg × factor
The adjustment factor is a practical multiplier for comparisons, not a lab correction. Keep it at 1.00 when you need strictly measured field results.
How to use this calculator
- Insert a ring a few centimeters into the soil surface.
- Pour water to a marked level and start timing.
- Record the water level drop after a fixed duration.
- Repeat 2–3 runs near the same spot for averaging.
- Enter the ring diameter (or custom area), then your run readings.
- Press Calculate to see rates, volume, and guidance.
- Use Download CSV or Download PDF to save results.
Why infiltration matters for irrigation
Infiltration rate describes how quickly water enters soil. When the applied watering rate exceeds infiltration, water ponds and runs off instead of reaching roots. Matching emitter output, hose flow, or sprinkler intensity to field infiltration reduces waste and erosion. Use the calculator’s average rate to size watering cycles and choose gentler application on slow sites.
Interpreting the measured rate
The calculator converts each run’s depth drop and time into millimeters per hour, then averages runs for a steadier estimate. Very slow results often indicate surface sealing, clay dispersion, or compaction. Very fast results are common in sandy beds or cracked dry ground and can increase nutrient leaching. Compare seasons and locations rather than relying on one test. For best consistency, use the same initial water depth, avoid obvious worm holes, and test after similar moisture conditions; extremely dry soil can crack and exaggerate early intake during the first minutes.
Using area and volume outputs
Ring diameter (or custom area) allows the tool to estimate infiltrated volume per run. Volume helps translate rates into practical water amounts: liters absorbed during a typical cycle, or how much water a planting zone can take before runoff begins. For small plots, volume is useful when filling watering cans or calibrating drip lines.
Adjustment factor for field comparison
The optional factor is a controlled multiplier for quick scenario comparisons. For example, mulched soil may behave better than bare soil under the same test depth, while crusted surfaces can behave worse. Keep the factor at 1.00 for pure measurements, and apply modest changes only when you document the reason in Notes for repeatable tracking.
Improving infiltration in gardens
Improve infiltration by reducing compaction, increasing stable aggregates, and protecting the surface. Add compost, keep living roots, and mulch to soften raindrop impact. Avoid working soil when wet, and consider broadforking or aeration where traffic is unavoidable. Retest after amendments; even a small increase in rate can lower runoff risk on sloped beds.
FAQs
What water depth drop should I record?
Use a clear start mark and measure the drop after a fixed time, such as 10 minutes. A 5–25 mm drop works well in many gardens, but any measurable change is acceptable.
Why do my runs show different rates?
Small differences are normal. Soil has channels, roots, and compacted patches. The first run can wet and swell fine particles, slowing later runs, while cracks can speed early intake. Averaging multiple runs gives a steadier value.
Should I use the adjustment factor?
Keep it at 1.00 for true field measurements. Use the factor only for controlled comparisons when you clearly note why the site should behave better or worse than the measured condition.
How do I read results in inches per hour?
Select inches as the depth unit before calculating. The tool will display both mm/hr and in/hr for the key rate outputs.
What infiltration range is generally workable for beds?
Many productive beds perform well in the moderate range, roughly 15–60 mm/hr, because water enters without long ponding. Slower soils need gentler, longer cycles. Faster soils benefit from mulch and split watering to reduce leaching.
Can I use this to plan for storms?
It helps gauge runoff risk, but it is not a full stormwater design method. Compare your infiltration rate to expected rainfall intensity, and prioritize surface cover, contouring, and overflow paths where rates are low.