⚗️ pH Calculator

Convert between pH, hydrogen ion concentration [H⁺], and hydroxide ion concentration [OH⁻]. Understand the pH scale with real-world reference examples.

pH value

Or enter [H⁺] concentration (mol/L)

Temperature correction

pH 7

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pH Reference Scale

pH	Example	Category
0–1	Battery acid, HCl (concentrated)	Strong acid
2	Stomach acid, lemon juice	Strong acid
3	Vinegar, cola, apple juice	Moderate acid
4	Tomato juice, beer, acid rain	Moderate acid
5	Black coffee, bananas	Mild acid
6	Milk, urine (typical), saliva	Mild acid
7	Pure water (neutral)	Neutral
8	Seawater, baking soda solution	Mild alkaline
9	Baking soda, antacids	Mild alkaline
10	Milk of magnesia, soapy water	Moderate alkaline
11	Ammonia (household cleaner)	Strong alkaline
12	Soapy water, lime water	Strong alkaline
13–14	Bleach, oven cleaner, NaOH	Very strong alkaline

📐 The logarithmic scale: pH is a logarithmic scale — each unit represents a 10× change in hydrogen ion concentration. pH 4 is 10× more acidic than pH 5, and 100× more acidic than pH 6. This is why the difference between pH 4 and pH 6 in acid rain is ecologically enormous.

🌱 Soil pH for gardening: Most plants prefer pH 6.0–7.0. Blueberries need pH 4.5–5.5 (acidic). Brassicas prefer pH 7.0–7.5. Test soil pH with strips or a meter. Acidify with sulphur; alkalinise with garden lime. Hydroponics: target pH 5.5–6.5 for optimal nutrient uptake.

🐟 Aquarium pH: Freshwater fish: pH 6.5–7.5. Marine aquariums: 8.1–8.4. African cichlids: 7.8–8.5. A drop of 0.5 pH units overnight is dangerous to fish — change water slowly and buffer where needed. CO₂ injection lowers pH; aeration raises it.