Water Bath Canning Time Calculator
Calculate USDA water bath canning times adjusted for altitude, jar size, and food type.
Covers jams, pickles, tomatoes, and fruit in pint and quart jars.
Water bath canning fundamentals:
Water bath canning is safe ONLY for high-acid foods (pH 4.6 or below). The boiling water (100°C / 212°F at sea level) is hot enough to kill molds, yeasts, and acid-tolerant bacteria in acidic environments but NOT hot enough to kill Clostridium botulinum spores — which is why low-acid foods MUST use pressure canning instead.
Safe foods for water bath canning:
| Food Category | Typical pH | Safe? | Examples |
|---|---|---|---|
| Fruits | 2.5–4.5 | Yes | Peaches, pears, apples, berries |
| Pickles (vinegar) | 2.5–3.5 | Yes | Cucumbers, beets, peppers |
| Jams/jellies | 3.0–3.5 | Yes | Any fruit preserve |
| Tomatoes (acidified) | 4.0–4.6 | Yes* | *Must add lemon juice or citric acid |
| Salsa (tested recipe) | 3.5–4.2 | Yes | Only USDA-tested recipes |
| Vegetables (plain) | 5.0–6.5 | NO | Must pressure can |
| Meat/poultry | 5.5–6.5 | NO | Must pressure can |
Base processing times (sea level):
| Food | Pint (500 ml) | Quart (1 L) |
|---|---|---|
| Peaches (hot pack) | 20 min | 25 min |
| Pears (hot pack) | 20 min | 25 min |
| Applesauce | 15 min | 20 min |
| Dill pickles | 10 min | 15 min |
| Bread & butter pickles | 10 min | 15 min |
| Strawberry jam | 10 min | — |
| Grape jelly | 5 min | — |
| Tomatoes (acidified) | 35 min | 45 min |
| Salsa | 15 min | — |
Altitude adjustment formula:
At higher altitudes, water boils at lower temperatures, so processing time must increase:
| Altitude | Adjustment |
|---|---|
| 0–305 m (0–1,000 ft) | No change |
| 306–915 m (1,001–3,000 ft) | +5 minutes |
| 916–1,830 m (3,001–6,000 ft) | +10 minutes |
| 1,831–2,440 m (6,001–8,000 ft) | +15 minutes |
| > 2,440 m (> 8,000 ft) | +20 minutes |
Example calculation:
Canning peaches in quart jars at 1,200 m (4,000 ft) elevation:
- Base time: 25 minutes (quart, hot pack)
- Altitude adjustment: +10 minutes (916–1,830 m range)
- Total processing time: 35 minutes
Critical safety rules:
- Start timing ONLY after the water reaches a full rolling boil
- Keep jars covered by at least 2.5 cm (1 inch) of water throughout processing
- Never reduce processing times from tested recipes
- Let jars cool undisturbed for 12–24 hours after processing
- Check seal by pressing the center of the lid — it should not flex
- Any jar that does not seal must be refrigerated and used within 2 weeks
Water volume estimation:
You need enough water to cover jars by 2.5 cm plus 5 cm of headspace to prevent boiling over:
Water needed (liters) ≈ Canner diameter² × 0.785 × (Jar height + 7.5 cm) / 1000