Rainfall Converter — mm to Inches, Precipitation Depth

Precipitation depth is how much rain, snow melt, or water equivalent accumulated over a period — measured as a vertical depth in a rain gauge. Most of the world reports rainfall in millimeters; the United States commonly uses inches. This converter switches between mm, cm, and in from one input.

When you read a foreign forecast or compare a local gauge to an imperial datasheet, the conversion uses one exact factor: 1 inch = 25.4 mm. All math runs locally in your browser.

WMO and national meteorological agencies define daily and monthly totals in mm (or cm for large seasonal sums):

1 inch = 25.4 mm  ·  1 cm = 10 mm  ·  mm = inches × 25.4

Divide mm by 25.4 for inches; multiply inches by 25.4 for mm. Centimeters fit large totals: 100 mm = 10 cm = 3.94 in.

• 1 mm ≈ 0.04 in — light drizzle total
• 10 mm ≈ 0.39 in — moderate shower
• 25.4 mm = 1.00 in — exact inch reference
• 50 mm ≈ 1.97 in — often classed as heavy rain in 24 h
• 100 mm ≈ 3.94 in — very wet day
• 250 mm ≈ 9.84 in — extreme daily totals
• 1,000 mm = 100 cm ≈ 39.4 in — rough annual total for wet climates

Precipitation depth is accumulation in a gauge over a stated interval (1 h, 24 h, month, year). A report of "50 mm in 24 hours" is depth; "50 mm/h" is intensity — a different measurement.

This tool handles mm, cm, and inches of accumulation only. One liter per square meter equals one millimeter of water depth. Snow is often reported as depth or water equivalent in mm — once expressed as liquid-equivalent depth, use the same formulas. For general length beyond precipitation, see the Length & Distance Converter.

Weather forecasts quote expected totals in mm or inches for the next 24 h or storm window. Rain gauges record depth — home stations may display inches while national networks publish mm. Climate normals and agricultural planning use annual rainfall in mm or inches; converting helps when comparing regions.

Hydrology design storms are often quoted in mm. An imperial brief stating "3 inches in 24 h" becomes 76.2 mm for metric spreadsheet work.

Many services flag at least 50 mm in 24 h as heavy rain (~2 in). Flash-flood guidance may cite 25 mm in 1 h or 75 mm in 6 h depending on terrain. Converting units does not change the physical amount — it only expresses the same depth in mm, cm, or inches.

Pair rainfall depth with wind from the Wind Speed Converter when reviewing storm briefings.

50 mm → inches: 50 ÷ 25.4 = 1.97 in

2 in → mm: 2 × 25.4 = 50.8 mm

15 cm → inches: 150 mm ÷ 25.4 = 5.91 in

0.5 in → mm: 0.5 × 25.4 = 12.7 mm