Abstarct: In all industries, national labs, university research centers, plants(factories) and all the units using flow meter , using a precise flow meter is inevitable and measurement is considered as a critical issue. One of the important applications of flow meters is household gas consumption to which a large portion of the over-all produced gas is allocated. Thus, to achieve this goal we thought of a new kind of flow meter, called capillary thermal mass flow meter for household consumption. The structure of this flow meter compared to the existing diaphragm flow meter is much simpler. In addition, fixed components, less periodic repair and higher precision are the other strong points of this device. This flow meter follows the first law of thermodynamics that consists of laminar flow element and a sensor tube with has central heater and two sensors are located upstream and downstream of the heater.in this way, using the thermal flux into the sensor tube to caculate the temperature difference and flow rate. Using 3.12 advanced code version AVR to calculate heat difference and via PT100 sensor is assigned on tube for sencing. Thus, we designed and built this type of flow meter according to the national gas standards with the use of the currently available elements in the market. Then in calibration units, we calibrated household gas counters. Finally, we analyzed the results, problems and obstacles we faced. Moreover, we came up with new equation to calculate the uncertainty of the flow meter. Calibration factor is derived 0.08 and the flow meter is suitable up to 1.2 cubic meter per hour.