Rain gauge sizes and diameters
/Rain gauges come in many different sizes and shapes. The following table lists the most common sizes, opening areas, and diameters in inches and centimeters. Rain gauges are also known as precipitation gauges, udometers, pluviometers, ombrometers, and rain sensors.
| Rain Catchment Opening Area | Rain Opening Diameter | ||||
|---|---|---|---|---|---|
| Common name | cm² | in² | cm | in | Common resolutions |
| 200 square centimeter rain gauge | 200 | 31.0 | 16.0 | 6.284" | 0.2 mm, 0.1 mm |
| 8 inch rain gauge | 325 | 50.4 | 20.3 | 8.011" | 0.254 mm (0.1"), 0.2 mm |
| 400 square centimeter rain gauge | 400 | 62.0 | 22.6 | 8.887" | 0.2 mm, 0.1 mm, 0.254 mm (0.1") |
| 500 cm2 or 10 inch rain gauge | 500 | 77.5 | 25.2 | 9.936" | 0.2 mm, 0.1 mm, 0.254 mm (0.1") |
| 533 square centimeter rain gauge | 533 | 82.6 | 26.1 | 10.256" | 0.075 mm |
| 800 square centimeter rain gauge | 800 | 124.0 | 31.9 | 12.568" | 0.2 mm, 0.1 mm |
| 1000 square centimeter rain gauge | 1000 | 155.0 | 35.7 | 14.052" | 0.2 mm, 0.1 mm |
Manufacturer datasheets usually state rain-gauge calibration accuracy, not field accuracy. With a few exceptions, such as the wireless MeteoRain IoT series, the accuracy of most rain gauges, apart from weighing rain gauges, is tied to rain intensity. Manufacturers therefore state rain-gauge accuracy at prescribed rain-intensity rates. This is useful for comparing best-case measuring-mechanism accuracy, but it falls far short of field accuracy, because rain intensity varies and dirt effects on measuring mechanisms, as well as temperature-related instabilities in weighing rain gauges, are not accounted for.
Industry examples commonly tie the stated accuracy (measurement uncertainty) to a specific rain intensity—such as ±1–2% at about 24–50 mm/h, ±2% at 30 mm/h, or ±2% to 200 mm/h and ±3% to 380 mm/h—while cleaning, annual checks, or field verification are listed separately. [1] It is important to note that many instruments are calibrated with a trade-off: rain accumulation can be overstated at low intensities below 10 mm/h so that under-measurement at higher rain rates is reduced.
Outdoors, additional uncertainty is set by physics rather than brand: wind alters airflow at the orifice and therefore catch efficiency, while splash, wetting, and water retained on collector surfaces reduce or delay the water reaching the sensor. [2] Thus, the aerodynamics of the rain-gauge funnel and splash guards play a vital role in field performance and accuracy, especially where variable rain intensities are encountered.
WMO guidance accordingly calls for collector geometries that minimize splash, wetting, and evaporation, and it recognizes the benefit of shielding where wind is important. [3] This is especially true in regions where drizzle is common or where coastal fog contributes materially to rain accumulation, and in most regions around the world where wind usually accompanies rain.
Peer-reviewed studies likewise show that laboratory-to-field differences are driven not only by exposure but also by the time-varying dynamics of real storms, which is why some modern gauges use flow-dependent or interval-based correction instead of one static calibration value. [4]
In that context, BARANI’s MeteoRain 200 Pro, 400 Aero, and 533 Classic datasheets are notable for reporting “field performance” and for explicitly adding a starting-threshold term that includes trapped water and the wetting of dirt, dust, and debris. That does not change the physics, but it does make the published accuracy closer to the way rain gauges are actually used in the field. [5]
References
[1] Casella Tipping Bucket Rain Gauge datasheet; Royal Eijkelkamp Rain Gauge datasheet; Texas Electronics TR-525M; NESA PL400; Observator RIM-7499-BOM.
[2] Pollock et al., Quantifying and Mitigating Wind-Induced Undercatch in Rainfall Measurements; WMO No. 8 training material on splash and wetting errors.
[3] WMO No. 8 (2024, Vol. I, Ch. 6) training slides on shielding, rim/orifice geometry, splash, wetting, and evaporation.
[4] Colli et al. (2014) on dynamic laboratory testing of weighing and tipping-bucket gauges; Sypka et al. (2019) on real-time volumetric correction for tipping-bucket gauges.
[5] BARANI MeteoRain 200 Pro, 400 Aero, and 533 Classic datasheets.