Calculator Servicescalculatorservices.com

Relative Humidity Calculator

RH from air temp and dew point. Free online Relative Humidity Calculator. Calculate relative humidity online — fast, accurate, mobile-friendly, no signup needed

RH (%)
53.8306%

Derivation

  1. ├── 01GivenT = 25, Td = 15
  2. ├── 02Formula100 × exp(17.625 × a / (243.04+a)) / exp(17.625 × t / (243.04+t))
  3. └── 03Compute RH (%)53.830642
Did you know?

Every calculator here runs 100% in your browser — nothing is sent to a server or stored in a database.

§01What is

Understanding the Relative Humidity Calculator

The Relative Humidity Calculator computes RH (%) from 2 inputs: air t (°c), dew point (°c). RH from air temp and dew point.

Quick calculators for the math that shouldn’t need a notepad — instant, accurate, private to your browser. The Relative Humidity Calculator sits in that toolkit — it RH from air temp and dew point. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

100 × exp(17.625 × a / (243.04+a)) / exp(17.625 × t / (243.04+t))

Where

T
Air T (°C)
Td
Dew point (°C)
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Air T (°C) = 25, Dew point (°C) = 15.

  1. 01Start by noting the input — Air T (°C): 25.
  2. 02Start by noting the input — Dew point (°C): 15.
  3. 03Substitute these values into the formula: 100 × exp(17.625 × a / (243.04+a)) / exp(17.625 × t / (243.04+t))
  4. 04Compute RH (%): the calculator returns 53.8306.
  5. 05Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Relative Humidity Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Air T (°C) halved

T = 12.5 (from 25)

Keep every other input at its default and halve the air t (°c). See how rh (%) responds.

  1. 01New Air T (°C): 12.5
  2. 02Baseline RH (%): 53.8306
  3. 03New RH (%): 117.634
  4. 04RH (%) increases by 118.5% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Air T (°C) doubled

T = 50 (from 25)

Keep every other input at its default and double the air t (°c). See how rh (%) responds.

  1. 01New Air T (°C): 50
  2. 02Baseline RH (%): 53.8306
  3. 03New RH (%): 13.7694
  4. 04RH (%) decreases by 74.4% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Dew point (°C) halved

Td = 7.5 (from 15)

Keep every other input at its default and halve the dew point (°c). See how rh (%) responds.

  1. 01New Dew point (°C): 7.5
  2. 02Baseline RH (%): 53.8306
  3. 03New RH (%): 32.75
  4. 04RH (%) decreases by 39.2% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Dew point (°C) doubled

Td = 30 (from 15)

Keep every other input at its default and double the dew point (°c). See how rh (%) responds.

  1. 01New Dew point (°C): 30
  2. 02Baseline RH (%): 53.8306
  3. 03New RH (%): 133.998
  4. 04RH (%) increases by 148.9% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
Your feedback

How useful was this calculator?

Your ratings stay in your browser — they help us learn which tools people actually rely on.

Rate it
Was this helpful?