---
title: Grow room sensor accuracy and calibration | Grow Sensor
description: "Every Grow Sensor PRO is calibrated in a test chamber before it
  ships: leaf ±0.5 °C, air ±0.1 °C, humidity ±1 %RH. What drifts, and how to
  keep it honest."
url: https://growsensor.co/accuracy
---

Accuracy

# Calibrated before it leaves us.

Every Grow Sensor PRO is calibrated in our test chamber before it ships, light included, so every room is measured against the same reference. Below: how close each reading is, and what needs checking over time.

 [See the specs](#specs)

By [Tom Starley](https://growsensor.co/team/tom-starley), founder of Grow Sensor · updated 13 November 2026

[Image: GS-01, the Grow Sensor PRO: matte white instrument with a vented base, head-on studio render]

Spec sheet

## How close each reading is.

Air, leaf, CO₂ and light each have their own sensor. Small numbers matter: at 26 °C, every 1 % of humidity error moves VPD by about 0.03 kPa.

| Channel | How it's measured | Range | Accuracy |
| --- | --- | --- | --- |
| Climate |
| Air temperature | Sensirion SHT45, digital | −9–58 °C | ±0.1 °C |
| Humidity | Sensirion SHT45, capacitive | 10–95 %RH | ±1 %RH (typical) |
| CO₂ | NDIR | 400–5000 ppm | ±(40 ppm + 5 %) |
| Plant |
| Leaf temperature | Infrared, read from the leaf | −30–100 °C | ±0.5 °C |
| Light |
| Spectrum | Multi-channel spectral sensor | 380–910 nm | ±2 nm a channel |
| ePPFD and ePAR | From the spectrum | 400–750 nm | Validated against Apogee |
| DLI | From ePPFD across the day |  | ±3 % |
| Root zoneProbes carry their makers' published specs. They don't go through our chamber. |
| Water content | SubSense | 0–100 % VWC | ±1.8 % (0–50 %) |
| Pore water EC | SubSense | 0–20 dS/m | ±5–10 % |
| Substrate temperature | SubSense | −40–85 °C | ±0.5 °C |
| Water content | METER Group SOLYX 14 | 0.00–0.72 m³/m³ | ±0.03 m³/m³ (±0.01 medium-specific) |
| Bulk EC | METER Group SOLYX 14 | 0–20 dS/m | ±(5 % + 0.1 dS/m) to 10 dS/m, ±8 % above |
| Substrate temperature | METER Group SOLYX 14 | −40–60 °C | ±0.3 °C (0–60 °C) |

In the chamber

## One chamber, every unit.

So when two rooms read differently, look at the rooms first.

1.  01

    Every unit, every channel.

    Each Grow Sensor PRO goes into a dedicated test chamber before it ships: air temperature, humidity, CO₂, leaf temperature and light.

2.  02

    Light against a reference.

    PPFD and PAR are calibrated in the same chamber and validated against Apogee, the quantum sensor growers benchmark against.

3.  03

    A record for every unit.

    Each PRO has its own full calibration record, so the numbers it starts with are on file.

Under the lights

## Built to read the air, not the lights.

Grow lights heat everything under them. A sensor that warms up reads the air too hot and too dry, and VPD reads high.

The PRO has no fan to fail, foul or bias the reading. Its case is passively cooled: a double wall with an air gap shields the sensors, like double glazing, and the shape draws cool air in through the base and lets heat out of the top.

Leaf temperature doesn't rely on the air at all. It's read by infrared, from the leaf.

[Image: GS-01 from the front: vents in the base and slots across the top of the case]

Cool air in at the base, heat out of the top. Not to scale.

Keeping it accurate

## What needs checking, and when.

CO₂ Needs routine calibration. Sensitive to shock.

Calibrate every 3 to 6 months, and after a drop. Outdoors in fresh air, started from the unit's button, in about two minutes.

Temperature, humidity and light Drift should be minimal.

No routine calibration. Optional offsets for air and leaf temperature in the app. Check humidity against a Boveda 75 % kit only if a verified reference disagrees.

Step-by-step guides are on [our help site](https://faq.growsensor.co/the-grow-sensor/how-do-i-calibrate-the-grow-sensor).

Questions

## What growers ask about accuracy.

The Grow Sensor PRO reads air temperature to ±0.1 °C and humidity to ±1 %RH (typical) with a Sensirion SHT45, leaf temperature to ±0.5 °C by infrared, CO₂ to ±(40 ppm + 5 %) by NDIR, and DLI to ±3 %, with PPFD validated against Apogee. Every unit is calibrated in our test chamber before it ships.

CO₂ needs calibrating every 3 to 6 months, and after a unit is dropped: outdoors in fresh air, started from the unit's button, in about two minutes. Temperature, humidity and light need no routine calibration, and optional offsets in the app cover fine-tuning.

It's built to limit it. The Grow Sensor PRO has no fan and is passively cooled: a double wall with an air gap shields the sensors, and the case draws cool air in at the base and lets heat out of the top. Leaf temperature is read by infrared, from the leaf.

Every Grow Sensor PRO is calibrated in the same test chamber before it ships, light included, and each has its own calibration record. That is what makes readings comparable from room to room.

Yes. The app has optional offsets for air temperature, leaf temperature and CO₂, and humidity can be checked against a Boveda 75 % calibration kit. Adjust only when a verified reference disagrees.

## Stop guessing. Start measuring.

Sixty-day money-back guarantee. Two-year warranty. Free app included.

Ready to buy? [Order Grow Sensor](https://growsensor.co/shop)