What Is Voltage-to-Pressure Conversion?
Most electronic pressure sensors don't output pressure directly — they output a small voltage. A transducer watching a 100 psi line might quietly report 2.5 V, and it's up to you to turn that number back into something meaningful. That translation is called voltage-to-pressure conversion, and it shows up everywhere: engine boost gauges, hydraulic systems, air compressors, and lab equipment all speak in volts while humans think in psi.
The good news: virtually all pressure transducers are linear devices. Double the pressure and the voltage doubles too. That means one simple straight-line equation converts every possible reading — no charts, no guesswork.
The Formula
Because the relationship is linear, any sensor is fully described by two numbers — a slope and an offset:
[
\text{Pressure} = \text{slope} \times V_{\text{reading}} + \text{offset}
]
where the slope comes from the sensor's rated range and voltage span:
[
\text{slope} = \frac{P_{\text{range}}}{V_{\text{upper}} - V_{\text{lower}}}
\qquad
\text{offset} = -,\text{slope} \times V_{\text{lower}}
]
Written as a single expression, this is the form most datasheets imply:
[
\text{Pressure} = P_{\text{range}} \times \frac{V_{\text{reading}} - V_{\text{lower}}}{V_{\text{upper}} - V_{\text{lower}}}
]
Where:
- Prange is the total measurable pressure span of the sensor.
- Vreading is the voltage you measured.
- Vlower is the voltage at zero pressure.
- Vupper is the voltage at maximum pressure.
Worked Example: A 0.5–4.5 V Sensor
Say you have a very common industrial sensor: it measures 0–100 psi and outputs 0.5 V at zero pressure and 4.5 V at full scale. Your meter reads 2.5 V.
First find the slope and offset:
[
\text{slope} = \frac{100}{4.5 - 0.5} = 25 \text{ psi/V}
\qquad
\text{offset} = -25 \times 0.5 = -12.5 \text{ psi}
]
Then apply the line to your reading:
[
\text{Pressure} = 25 \times 2.5 - 12.5 = 62.5 - 12.5 = 50 \text{ psi}
]
Sanity check with the ratio form: (100 \times \frac{2.5 - 0.5}{4.5 - 0.5} = 100 \times \frac{2}{4} = 50) psi. Both routes agree — halfway through the voltage span is halfway through the pressure range, exactly what a linear sensor should do.
| Parameter | Value |
|---|---|
| Pressure range | 100 psi |
| Voltage lower limit | 0.5 V |
| Voltage upper limit | 4.5 V |
| Voltage reading | 2.5 V |
| Slope | 25 psi/V |
| Offset | −12.5 psi |
| Calculated pressure | 50 psi |
Interpreting the Calibration Line
Once you know the slope and offset, you own the whole sensor:
- Slope tells you the resolution: at 25 psi/V, every 0.04 V of change is 1 psi. If your voltmeter only reads to 0.1 V, you can never resolve better than 2.5 psi with this sensor.
- Offset tells you why live-zero matters. At exactly 0.5 V the line correctly reads 0 psi — but a dead wire reading 0 V would compute −12.5 psi, an obviously impossible value that flags the fault immediately.
- Out-of-range readings mean trouble. Below 0.5 V or above 4.5 V the sensor is outside its guaranteed accuracy, so treat anything computed there as an estimate, not a measurement.
Try the calculator above with your own sensor's numbers — the result line shows the slope and offset so you can convert every future reading in your head.
If you're working through sensor fundamentals next, the pressure sensor accuracy calculator is a natural next step for judging how trustworthy your readings really are.