The pH Scale
Free printable pH scale diagram — the 0 to 14 scale colored from acidic red to basic purple, with the neutral point at 7. Download a high-resolution PDF or PNG for Letter paper.
Reading the pH scale
The pH scale measures how acidic or basic a liquid is, from 0 to 14. Low numbers are acidic, 7 is neutral, and high numbers are basic (also called alkaline). Here is what happens at each labeled part of the diagram:
| Range | What it does | Why it matters |
|---|---|---|
| Acidic (0–6) | Acids such as lemon juice, vinegar and stomach acid. The lower the number, the stronger the acid. | Your stomach relies on a very strong acid (around pH 2) to break down food and kill harmful bacteria — without it, digestion would stall and dangerous microbes could survive. Acids in everyday foods like citrus fruit and yogurt also give them their sharp, tangy flavor. |
| Neutral (7) | Neither acidic nor basic. Pure water is neutral. | Pure water sits at the exact midpoint because it carries no extra acid or base — which is exactly why your body uses it to safely transport nutrients and waste without triggering unwanted reactions. If your blood drifted even slightly away from near-neutral, your cells would start to shut down. |
| Basic / alkaline (8–14) | Bases such as baking soda, soap and bleach. The higher the number, the stronger the base. | Strong bases like bleach work by chemically breaking apart the molecules in grease and germs, which is why they're powerful cleaners — but also why they're dangerous to touch or swallow. Even a mild base like baking soda reacts with acids in cooking, releasing bubbles of carbon dioxide that make cakes rise. |
| The full scale (0–14) | It runs from 0 (most acidic) to 14 (most basic). Each step is ten times stronger than the one before it. | Because each step on the scale is ten times stronger than the last, the jump from pH 7 to pH 5 isn't a small shift — it's a hundred times more acidic. That exponential jump is why a tiny spill of battery acid (near pH 0) is far more dangerous than vinegar (pH 3), even though they're only a few numbers apart. |
Companion worksheet
A free fill-in worksheet with an answer key, built from the labels above — students match each range to its description, then answer a couple of short questions. Great for a quick check after using the diagram.
How to print
Choose Download PDF for a ready-to-print file that fits US Letter paper (8.5 × 11") in landscape, or Download PNG for the high-resolution image.
Frequently asked questions
What does the pH scale measure?
It measures how acidic or basic a liquid is, on a scale from 0 to 14. Below 7 is acidic, 7 is neutral, and above 7 is basic (alkaline).
What is a neutral pH?
A pH of 7 is neutral — neither acidic nor basic. Pure water has a pH of 7.
What paper size should I print this on?
The diagram is sized for standard US Letter paper (8.5 × 11") in landscape orientation. Use "Download PDF" for a print-ready file that fits the page automatically.