About us

Why it exists

Plenty of VPD calculators exist, and many of them get the basics wrong. Some show air VPD and call it leaf VPD. Some give one target range in a table and a different one in the text. Some ask for an email address before they show you a chart.

This site does the sums properly and shows its working. It tells you the exact humidity or temperature to set, not just a colour. It works the same on a phone in the grow room as on a desktop.

What is here

The VPD calculator with a live chart, plus 14 more tools: a printable VPD chart, leaf VPD, dew point, a dew point chart, wet bulb, dehumidifier and humidifier size, exhaust fan, air conditioner, CO₂, grow light, electricity cost, plant spacing and DLI. They all use the same calculation code, so the same inputs give the same answer on every page.

How the numbers are kept honest

• Every formula and every target range comes from a published reference, listed under Sources at the bottom of each calculator.
• Hundreds of automated tests run on every change. They compare each calculator's output with the formulas, and check that the site works on phones, in both colour themes and with a keyboard.
• Target ranges are starting points. Strains, crops and rooms differ, so watch your plants and adjust.

What it will never do

• No ads, no affiliate links and no sponsored products. Nothing on the site is for sale.
• No sign-up and no tracking. What you type stays in your browser; see the Privacy Policy.

Put the calculator on your site

Run a grow blog or forum? Paste this where you want a small VPD calculator. It is free, has no tracking and links back here.