Measure your thermos and pick a shape today. Enter units, thickness, and target fill level. Get capacity instantly, then export results for records later.
| Use case | Shape | Outer size | Fill % | Estimated capacity |
|---|---|---|---|---|
| Short garden session | Cylinder | Diameter 70 mm, Height 210 mm | 95% | ~0.77 L usable |
| Half-day watering | Cylinder | Diameter 80 mm, Height 260 mm | 90% | ~1.18 L usable |
| Hot tea for pruning | Cylinder | Diameter 73 mm, Height 300 mm | 85% | ~1.02 L usable |
Garden work often mixes sun, wind, and steady movement, so hydration needs rise quickly. A correctly sized thermos prevents early fatigue and reduces trips back indoors. Capacity also affects how long drinks stay warm or cold because larger volumes lose temperature more slowly when the lid is opened less often. Shade breaks and salty snacks can dull thirst cues, so plan intake deliberately. A snug fit in a backpack side pocket matters when moving through beds all day.
Manufacturers usually quote nominal volume, but real internal space depends on wall thickness, base thickness, and the lid’s inner stopper. This calculator subtracts those allowances to estimate internal volume, then applies a fill percentage for safe headspace. That approach mirrors practical use with hot tea, electrolyte water, or compost‑mix drinks.
Most bottles behave like cylinders, while boxy lunch canisters match rectangular geometry. Round canisters can be treated as spheres when they are close to perfectly round. If your thermos tapers, averaging top and bottom diameters keeps the estimate close, especially when the taper is gentle and the height remains constant.
The output shows liters and milliliters for precision, plus cups and fluid ounces for quick planning. For example, 1,000 mL equals 1 L, and many people drink 250–350 mL per break. Use the usable volume value when you leave headspace, or when ice occupies part of the interior.
For light tasks like deadheading, 0.6–0.9 L is often enough. For longer watering, pruning, or lawn edging, 1.0–1.5 L reduces refill breaks. In very hot weather, consider two smaller bottles rather than one large bottle, so one stays sealed and colder. Export results to track which size fits each season.
Use outer measurements when you do not know the interior size. Enter wall, base, and lid allowances to approximate the inner cavity. If you can measure the inner cavity directly, set allowances to zero.
For hot liquids, 90–95% is usually safer. It leaves headspace for expansion, prevents splashes when walking, and reduces pressure around stoppers. Use a lower fill if you add tea bags or infusers.
A mild taper is fine. Measure top and bottom diameters, take the average, and treat it as a cylinder. If the taper is strong, your estimate may drift; in that case, measure the inner volume with water for confirmation.
Volume depends on squared radius for cylinders and cubed radius for spheres. Small changes to internal radius remove a lot of space. That is why insulated walls and thick bases reduce real capacity compared with labeled volume.
Choose the unit that matches your measuring tool so you avoid conversion errors. The calculator converts internally to centimeters, then outputs liters, milliliters, cups, and fluid ounces. Consistency across inputs matters more than the unit itself.
Fill the thermos with measured water using a kitchen jug, then compare the poured volume to the calculated total. Repeat at your chosen fill percentage. This check is useful when the interior shape is irregular.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.