Estimated snowfall (inches) from liquid precipitation (inches)
| Liquid precipitation (inches) | 0.5 |
|---|---|
| Snow-to-liquid ratio | 10 |
| Estimated snowfall (inches) | 5 |
| Snowfall at the 13:1 reference ratio | 6.5 |
Common error: Applying the default 10:1 ratio regardless of temperature. Very cold air and near-freezing, wetter conditions produce meaningfully different ratios for the identical liquid precipitation, and a flat default can misstate the estimate substantially in either direction.
Snow-to-Liquid Ratio: formula
National Weather Service: Heat Index and Wind Chill · NWS La Crosse: Snow ratios
A ratio is an assumption, not a snowfall forecast. A colder surface temperature alone does not determine crystal growth or make the ratio rise monotonically. Measured depth changes through settling and melting.
This calculation does not evaluate structural capacity, travel conditions or a snow-removal plan.
Enter liquid-water equivalent in inches and an assumed snow-depth-to-water ratio. The example 10:1 and the separate 13:1 result are comparison scenarios, not a claim that either ratio is a universal NWS average. Crystal growth, atmospheric profile, wind, compaction and melting affect the observed ratio.
Use the ratio associated with the actual forecast or measurement.
Snow-to-Liquid Ratio: changing Liquid precipitation (inches)
| Liquid precipitation (inches) | Estimated snowfall (inches) | Snowfall at the 13:1 reference ratio |
|---|---|---|
| 0.4 | 4 | 5.2 |
| 0.45 | 4.5 | 5.9 |
| 0.5 (example) | 5 | 6.5 |
| 0.55 | 5.5 | 7.2 |
| 0.6 | 6 | 7.8 |
Snow-to-Liquid Ratio: compare input ranges
| Input | Tested from | To | Estimated snowfall (inches): low input | Estimated snowfall (inches): high input | Swing |
|---|---|---|---|---|---|
| Liquid precipitation (inches) | 0.45 | 0.55 | 4.5 | 5.5 | 1 (20%) |
| Snow-to-liquid ratio | 9 | 11 | 4.5 | 5.5 | 1 (20%) |
Snow-to-Liquid Ratio: individual input comparisons
| Input | Value | Estimated snowfall (inches) | Snowfall at the 13:1 reference ratio |
|---|---|---|---|
| Liquid precipitation (inches) | 0.4 | 4 | 5.2 |
| 0.45 | 4.5 | 5.9 | |
| 0.5 | 5 | 6.5 | |
| 0.55 | 5.5 | 7.2 | |
| 0.6 | 6 | 7.8 | |
| Snow-to-liquid ratio | 8 | 4 | 6.5 |
| 9 | 4.5 | 6.5 | |
| 10 | 5 | 6.5 | |
| 11 | 5.5 | 6.5 | |
| 12 | 6 | 6.5 |
Estimated snowfall (inches): Liquid precipitation (inches) against Snow-to-liquid ratio
| Liquid precipitation (inches) / Snow-to-liquid ratio | 8 | 10 | 12 |
|---|---|---|---|
| 0.4 | 3.2 | 4 | 4.8 |
| 0.45 | 3.6 | 4.5 | 5.4 |
| 0.5 | 4 | 5 | 6 |
| 0.55 | 4.4 | 5.5 | 6.6 |
| 0.6 | 4.8 | 6 | 7.2 |
Snow-to-Liquid Ratio: values and definitions
| Quantity and definition | Value used |
|---|---|
| Liquid precipitation (inches) | 0.5 |
| Snow-to-liquid ratio — Entered snow-depth/liquid-water ratio. Ten-to-one is an example, not a universal forecast ratio. | 10 |
| Estimated snowfall (inches) | 5 |
| Snowfall at the 13:1 reference ratio | 6.5 |
Liquid precipitation (inches): half and double
| Liquid precipitation (inches) | Estimated snowfall (inches) |
|---|---|
| 0.25 | 2.5 |
| 0.5 | 5 |
| 1 | 10 |
The commonly cited 10:1 snow-to-liquid ratio is a rough national average, not a fixed law, and the real ratio swings well outside that range with air temperature: colder, drier air produces fluffy snow that can run 15:1 or higher, while wetter, near-freezing conditions can compact down closer to 5:1 for the identical liquid equivalent.
Adjust the ratio for the actual expected air temperature rather than defaulting to 10:1 regardless of conditions, especially in cold or marginal near-freezing weather.
See temperatures on the temperature converter, wind effects on the wind chill page, and roof loads in the trades and home categories. The percentage and proportion calculators help with scaling, and the degree days calculator relates to winter weather demand.
Does 6.5 inches at 13:1 weigh more than 5 inches at 10:1?
Not in these examples: both start with 0.5 inch liquid equivalent, so they contain the same initial water mass over the same area.
Does this estimate a safe roof load?
No. It converts water equivalent to depth under an entered ratio. Structural limits, drift and later weather are outside it.
What is a typical snow-to-liquid ratio?
A ten-to-one ratio can be used as an explicitly assumed example, but actual snow density varies with weather and compaction. Use a measured or forecast ratio applicable to the event. The arithmetic converts liquid depth and the chosen ratio; it does not forecast snowfall or structural loading.
Why is wet snow heavier?
Because it contains more water per inch of depth, so a lower ratio means more weight per inch on roofs and trees.
Why do snowfall forecasts change?
Because small changes in temperature and the storm track shift both the liquid amount and the ratio, and the resulting depth.