Services | Pressure Gauge Accurancy

The following tables define the ASME B40.1 accuracy grades. Accuracy of a pressure gauge may be expressed as percent of span or percent of indicated reading. Percent of span is the most common method. Percent of indicated reading is usually limited to precision test gauges and unless specifically spelled out, it may be assumed that an accuracy of ±½% means ±½% of span.

The information above is derived from B40.1 & B40.7 contained in ASME B40.100. Printed copies are available from ASME, Three Park Ave, New York NY 10016. You can visit their website at www.asme.org.

• Grade 4A gauges offer the highest accuracy and are calibrated to ±0.1% of span over the entire range of the gauge. The gauges are called laboratory precision test gauges and are generally 8½", 12" or 16" dials. These high-accuracy gauges may be temperature compensated. They must be handled carefully in order to retain accuracy.


• Grade 3A gauges are calibrated to an accuracy of ±0.25% of span over the entire range of the gauge. The gauges are called test gauges and are generally 4½", 6" or 8½" dials. The gauges are generally not temperature compensated.


• Grade 2A gauges are calibrated to an accuracy of ±0.5% of span over the entire range of the guage. These gauges are generally used by the petrochemical industry for process pressure measurement. They are often referred to as process gauges and are usually supplied as 4½" and 6" cases and are not temperature compensated.


• Grade 1A gauges are calibrated to an accuracy of ±1% over the entire range of the gauge. These gauges are high-quality industrial gauges and are supplied in 2½", 3½", 4½", 6" and 8½" sizes.


• Grade A gauges are calibrated to an accuracy of ±1% of span over the middle half of the scale and ±2% of span over the first and last quarters of the scale. These gauges are often referred to as industrial gauges and usually supplied in 2½", 3½", 4½" and 6" case sizes.


• Grade B gauges are calibrated to an accuracy of ±2% of span over the middle half of the scale and ±3% of span onver the first and last quarters of the scale. This accuracy of gauge represents the majority of manufactured and used for pressure measurement on water pumps, swimming pool filters, air compressors, filter regulations, etc. These gauges are often referred to as commercial or utility gauges and are supplied in 1½", 2", 2½", 3½" and 4½" case sizes.