Managing indoor humidity starts with knowing what it is. Most people notice the stickiness, the smell, the damp clothes — but don't know whether their indoor RH is 58% or 82%. That difference determines what action, if any, is needed.
The tool: digital hygrometer
A digital hygrometer measures relative humidity (RH) and temperature, expressed as a percentage. The healthy range for indoor air is 40–60% RH.
Digital hygrometers are widely available in India for ₹300–800. Entry-level units are typically accurate to ±5% RH; mid-range units to ±2–3% RH. Both are sufficient for home use.
What to look for when buying one
Accuracy specification. Look for ±3% RH or better. Avoid devices without a stated accuracy figure.
Display. Both humidity and temperature on the same screen. Some also show 24-hour minimum and maximum readings, useful for understanding overnight RH fluctuations.
Size. A small tabletop unit is sufficient.
Avoid. Combined hygrometer-humidifier or hygrometer-dehumidifier devices marketed as "smart" without a stated accuracy specification. The sensing component is often lower quality.
Where to place it
Height. Place at chest height, roughly 1–1.5 metres from the floor. Near the floor, air is cooler and reaches saturation at lower moisture levels, so RH reads higher. Near the ceiling, warmer air keeps readings lower. Chest height gives the most relevant reading.
Away from windows and exterior walls. These surfaces reflect outdoor conditions rather than the room's overall RH.
Away from the AC unit. The area around a vent reads lower. Place it at least 1–2 metres away.
Away from bathrooms and kitchens. Readings spike after a shower or cooking and then fall, giving a localised reading rather than the room baseline.
For multiple rooms. Moving one hygrometer between rooms over a few days is more useful than one fixed unit. The overnight bedroom reading matters most for health.
When to measure
First thing in the morning. Humidity rises overnight in a closed bedroom. The morning reading shows peak RH during the hours you're most exposed.
Before and after interventions. Check before and after running AC dry mode or opening windows to see whether it is working.
During and after cooking. Shows how much cooking raises RH and whether exhaust fans make a difference.
On a rainy day with windows closed. Your baseline monsoon RH without ventilation.
On a clear morning after rain. Shows how much moisture the building has absorbed and is releasing indoors.
Reading the numbers
| RH Range | Condition | Action |
|---|---|---|
| Below 30% | Too dry | Airways dry out, viruses survive longer on surfaces. |
| 30–40% | Dry but acceptable | No immediate action needed. |
| 40–60% | Target range | Optimal for health and belongings. |
| 60–70% | Elevated | Mould risk begins. Dust mites thrive. Ventilate or run AC dry mode. |
| 70–80% | High | Active mould risk. Consider a dehumidifier if sustained. |
| Above 80% | Very high | Conditions that damage furniture, electronics, and books. Dehumidification needed. |
What to do with the reading
RH consistently below 60%: Within range. No intervention needed. Recheck during peak monsoon.
RH consistently 60–70%: Addressable without a dehumidifier in most cases. See How to Reduce Humidity in a Room for practical steps.
RH consistently above 70% despite ventilation: A standalone dehumidifier is likely appropriate. See the Dehumidifier Guide for sizing and product options, or walk through a worked sizing example for Mumbai, Bengaluru, Delhi, Kolkata, or Chennai.
Device options available in India
Basic tabletop hygrometers (₹300–600)
The HTC-1 is the most widely available entry-level unit, sold through electronics shops and online. Accuracy: ±5% RH. Sufficient for understanding whether you're at 60% or 80%, but not for fine-grained monitoring.
Mid-range hygrometers (₹800–1,500)
The ThermoPro TP50 is available through Indian distributors. Accuracy: ±2–3% RH, ±1°C. Shows current readings plus 24-hour high/low records with a 10-second refresh rate. For most households this is the practical choice: accurate, simple to read, no app required.
The ThermoPro TP55 is the touchscreen version. Accuracy: ±2% RH, ±0.5°C. 4-inch backlit display. Priced around ₹1,200–1,500.
If you already own an air purifier
Dyson purifiers (all current India models including the HushJet HJ10) include temperature and humidity sensors, displayed on the LCD and in the Dyson Link app.
Philips 3000i series (AC2887 and related models) includes humidity and temperature sensors on the unit and in the Philips app.
Note: air purifier sensors sit near the machine's intake, so placement affects the reading. A dedicated hygrometer at chest height in the centre of the room is more accurate.
What to avoid
Unbranded units under ₹200 typically lack a stated accuracy specification. The reading may be off by 10–15% RH, which makes it unreliable for any practical decision.
FAQ
How often should I check my hygrometer?
Once or twice a day during monsoon. Weekly outside monsoon.
My hygrometer reads differently in different rooms. Which reading do I trust?
All are correct for their location. Rooms can differ by 10–15% RH depending on ventilation, sun exposure, and proximity to bathrooms or kitchens. The bedroom reading matters most for health.
Do I need to calibrate my hygrometer?
Drift is rarely enough to affect practical decisions. If precision matters, a salt calibration test at home takes about 8 hours using table salt and a sealed container.
What is the difference between relative humidity and absolute humidity?
Relative humidity is a percentage of how full the air is at a given temperature. Absolute humidity is the actual mass of water vapour in grams per cubic metre. For home monitoring, relative humidity is the relevant figure.
Is 60% RH safe?
60% is the upper limit of the recommended range. A brief peak of 62% on a rainy afternoon is different from a sustained 65% across three months of monsoon.
For what to do once you have your reading, see How to Reduce Humidity in a Room and the Personal IAQ Checklist.
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