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Snow-to-Water Ratio Calculator

Find out how fluffy or dense fresh snow is compared to its melted water content.

How it is calculated

The tool divides the depth of fresh snow by the depth of water it melts into: ratio = snow depth ÷ water equivalent, shown as x : 1 with one decimal. It also gives the reverse view, SWE % = water equivalent ÷ snow depth × 100, with two decimals. Both must be above zero. The two depths must be in the same unit. The centimetre/inch selector does not change the arithmetic, so it only labels your numbers. The snow depth is the depth of freshly fallen snow, and the water equivalent is the depth of liquid after melting the same sample. Snow cannot melt into more water than its own depth, so a water value larger than the snow depth gives no result. Equal values are accepted and give 1.0 : 1.

Worked example

A snowfall of 25 cm melts to 1.6 cm of water. Ratio: 25 ÷ 1.6 = 15.625, shown as 15.6 : 1, so 15.6 cm of snow for every 1 cm of water. Water share: 1.6 ÷ 25 = 0.064, which is 6.40%. The tool displays a ratio of 15.6 : 1 and a snow water equivalent of 6.40%. A ratio of 10 : 1 would correspond to a water share of 10%.

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Common mistakes

  • Mixing units, such as snow depth in centimetres and melted water in millimetres. 25 cm and 16 mm typed as 25 and 16 gives 1.6 : 1 instead of 15.6 : 1.
  • Entering the water equivalent as larger than the snow depth, for example 10 snow and 25.4 water after converting inches to centimetres on only one side. The tool treats this as impossible and shows no result.
  • Measuring the depth of settled or old snow instead of fresh snowfall. Compaction changes the ratio, so use the new snow of one event.
  • Reading the second figure as a ratio. SWE % is the water as a share of the snow depth, so a lower percentage means fluffier snow.
  • Treating one measurement as the average for a whole season. The ratio varies with temperature and storm type, so a single value is only for that sample.

About this calculator

The snow-to-water ratio (SLR) expresses how many inches (or centimeters) of fresh snow correspond to one unit of melted liquid water — a widely cited rule of thumb puts the average at 10:1, but the real ratio swings anywhere from about 6:1 for wet, dense snow near freezing to 30:1 or higher for the driest powder that forms in very cold air, since colder temperatures produce more elaborate, air-filled snow crystals that pack less water into the same depth.

Meteorologists at the National Weather Service and other forecasting agencies use the snow-to-water ratio to convert forecast liquid precipitation into an expected snowfall depth, since precipitation models predict water content far more reliably than snow depth directly. Ski resorts and skiers reference the same ratio to judge whether incoming snow will be light, dry powder or heavy, wet snow, and hydrologists use it in reverse, measuring snow depth to estimate the water content that will feed spring runoff.

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