How to Calculate Humidity
What is Humidity?
Relative Humidity Calculator helps contractors and tradespeople accurately size, spec, and estimate materials and systems.
Formula
RH = (Partial Pressure of Water Vapor / Saturation Pressure) × 100
Step-by-Step Guide
- 1Measure wet and dry bulb temperatures, look up from psychrometric chart
- 2Apply the formula using your project measurements
- 3Add required safety factors or waste allowances per code
Worked Examples
Input
70°F dry bulb, 60°F wet bulb
Result
RH ≈ 57% from psychrometric chart
Common Mistakes to Avoid
- ✕Not applying code-required safety factors or derating
- ✕Forgetting to account for waste and cut losses in material estimates
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