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Free hydroponics calculators built for home growers. Every tool here solves a specific problem we kept seeing in forums and DMs — usually the same handful of questions about EC, PPM, nutrient ratios, pH and lighting that catch beginners out and trip up experienced growers when they switch brands or systems. No signups, no email gates, no premium tiers. Bookmark whichever ones you’ll use, and keep them open on your phone next time you’re mixing a reservoir. |
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EC ↔ PPM Converter
Convert between EC and PPM with the right scale for your meter. Supports 500, 640 and 700 scales (Bluelab, Hanna, Truncheon and more) with instant two-way conversion. Open the tool → |
pH Up/Down Dosing Calculator
Get pH right without overshooting. Tells you how many ml of pH Up or pH Down to add based on your reservoir size, brand, and water hardness. Open the tool → |
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Nutrient Dilution Calculator
Work out exactly how much water to add — or how much stock to top up with — to hit your target EC. Two-way calculation for any reservoir size. Open the tool → |
Grow Light DLI Calculator
Pick the right LED size for your tent and crop. Calculates target PPFD, daily light integral, and recommended wattage — brand-neutral, no marketing spin. Open the tool → |
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Why we built these calculators
Hydroponics has a numbers problem. EC and PPM are reported on three different scales depending on your meter brand. Nutrient bottles list dosing in ml-per-litre but feeding charts use PPM. pH adjusters come in different strengths from different manufacturers. Light requirements get expressed in watts, lumens, PAR, PPFD and DLI — most of which aren’t directly comparable. For a beginner trying to follow advice from three different sources, this is exhausting. For an experienced grower switching equipment or moving from soil to hydro, it’s a constant low-level annoyance. Most online calculators are either tied to a specific nutrient brand (and biased accordingly), or so packed with options they’re harder to use than just doing the maths by hand. These tools are deliberately narrow. Each one solves a single common problem, asks for the minimum information needed, and gives you an answer you can act on in under 30 seconds. They run entirely in your browser — nothing is uploaded, nothing is tracked, no account required. |
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Hydroponics quick reference
A few numbers worth memorising before you reach for a calculator:
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Calculators help. The full picture helps more.
If you’re just starting out, our beginner’s guide Start Your Hydroponics Journey walks you through every decision in order — system, nutrients, lighting, monitoring, troubleshooting. The numbers stop feeling random once you understand what they’re doing. Browse our ebooks → |
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Got an idea for a tool we should build? If there’s a hydroponics calculation you keep doing manually, we’d like to know. Drop us a line and tell us what’s missing. |