Voltage to PPM Calculator

Converting an analog voltage reading to Parts Per Million (PPM) requires knowing your specific sensor type. There is no universal multiplier. This calculator provides three distinct mathematical models for the most common engineering applications: TDS water sensors, linear industrial outputs, and precision electronics drift.

1. Analog TDS Sensor Conversion (Gravity/DFRobot)

Total Dissolved Solids (TDS) sensors measure electrical conductivity. The relationship between the output voltage and the actual PPM concentration is non-linear. Furthermore, water conductivity changes by about 2% for every degree Celsius. You must compensate the raw voltage for temperature before running the conversion.

Step A: Apply Temperature Compensation

Step B: Apply Cubic Polynomial

2. Linear Interpolation (Industrial Sensors)

Many industrial sensors output a perfectly linear voltage mapped to a known concentration range. For example, a gas sensor might output 0V at 0 PPM and 5V at 1000 PPM. We use standard linear interpolation to find the exact concentration.

• Identify your sensor's minimum and maximum voltage boundaries.
• Identify the corresponding minimum and maximum PPM detection limits.
• Read the current voltage output.
• Apply the interpolation formula below to map the reading to the scale.

3. Arduino & IoT Gas Sensors (MQ Series)

Unlike linear sensors, popular IoT gas sensors like the MQ-2, MQ-3, and MQ-135 have a non-linear, logarithmic relationship with gas concentrations. They work by changing their physical resistance ($R_s$) when exposed to target gases like CO2 or Smoke.

Because your microcontroller cannot read resistance directly, the sensor module uses a voltage divider circuit with a load resistor ($R_L$). To find the exact PPM concentration from your analog voltage reading ($V_{out}$), the calculator first reverses Ohm's law to determine the physical resistance ($R_s$). It then compares this to your clean-air baseline ($R_o$) and isolates the PPM from the gas-specific power regression curve ($A$ and $B$).

4. Electronics Reference Drift

In precision electronics design, the stability of a voltage reference is measured in Parts Per Million. This represents the fractional change from the nominal voltage output. For instance, if a 5V reference drifts by 1 millivolt, that is a 200 PPM deviation. If you need to assess the tolerance limits of these components, try evaluating them with our PPM Accuracy Calculator.

Understanding Your Results

You cannot blindly multiply a voltage reading by a static number unless you are certain the sensor has a strictly linear output that starts at zero. If you are starting with a known concentration and need to calculate what voltage your sensor should output, you can use our PPM to Voltage Calculator to reverse the math.

For a complete catalog of engineering conversions, return to our Engineering Calculators directory.