Charger tools
Charger Wattage Calculator
Two jobs, kept apart on purpose. First: turn one row of your charger's output label into watts — that is a profile's ceiling, not a measured sustained power. Second: check two devices at once, using the maker's per-port allocation figures rather than the total on the box.
The most common error on charger labels is adding the profiles together. A charger listing 5V≈3A / 9V≈3A / 15V≈3A / 20V≈3A does not deliver 15 + 27 + 45 + 100 = 187 W. It offers one of those profiles at a time, so its rating is the strongest single row, here 100 W. This tool never sums profiles, and treating a page that does as unreliable is reasonable.
Read a charger
Pick the check you need. Nothing is calculated until every value in that panel is valid.
RequiredOne output row: voltage and currentOptionalDevice needs, charger rating and per-port output, folded into “More options”
Output of this profile
What this number is, and is not
Combined demand of the two devices
- First device—
- Second device—
- Combined demand—
Port by port
Assumptions and limits
A label figure is not a measurement. The number this page produces is the arithmetic of one output row. What a device actually draws, and how much of that reaches its battery, are separate questions that no label answers.
Mode A: one profile, one wattage
W = V × A, for a single output profile
A charger's output label lists profiles such as 5V≈3A, 9V≈3A, 15V≈3A, 20V≈3A. Each row is a negotiation option, and the device picks one. Multiply the row the device actually uses: 20 V × 5 A = 100 W. The figure is the port's ceiling for that profile — the charger is capable of it, which does not mean your device asks for it.
- Do not add rows. 5 V + 9 V + 15 V + 20 V is not a wattage any port produces.
- Do not read the total as a per-port number. A "100 W" charger with three ports is not 100 W on each.
- Do not treat the figure as sustained output. Real delivered power depends on the device's request, the cable, and thermal limits that appear nowhere on the label.
Mode B: two devices at once
When a second device is connected, the charger re-plans its ports. How it does so is described in the maker's own table, usually printed as rows such as "C1 + C2: 45 W + 20 W". That row is the only honest source for the split. Three rules follow, and this page encodes all three:
- The allocation table decides. If port 1 drops to 45 W when port 2 is in use, that is the figure that applies — not the 100 W printed on the box.
- A sufficient total is not a sufficient port. 100 W total for two devices totaling 65 W demand says nothing about whether the laptop port still meets the laptop's need.
- No table, no verdict. Without the allocation figures the answer is Needs verification. This page never outputs "incompatible", because a missing table is missing information, not a failed check.
| What you entered | What the answer can say | What it will not say |
|---|---|---|
| Per-port figures from the table | Whether each port still covers its device | A prediction of charging speed |
| Total rating only | That the total is or is not enough as context | That either port meets its device |
| Nothing beyond device demand | Needs verification, and what to look up | That the combination fails |
Worked example
A 100 W two-port charger documents "C1 + C2: 45 W + 20 W". A laptop rated 60 W and a phone rated 20 W are connected. The phone port meets its need at 20 W. The laptop port delivers 45 W against a 60 W target — a documented per-port limit, and the reason a bigger single-port charger or a different port combination matters. Nothing in that example depends on the 100 W total, which is why the total is treated as context only.
Where the device figure comes from
The demand side comes from the device itself: its original power supply, the spec sheet, or the input rating printed on the device. Using the charger's maximum as the device's demand is the second most common error on this subject — it makes every charger look adequate and every laptop look underpowered at the same time.
Related
- 65W vs 100W charger — when the higher rating changes anything at all.
- Laptop and phone on one charger — the same rule applied to a travel kit, with the minimum parts list.
- USB-C charging cable guide — the cable is often the real ceiling above 60 W.
- How we calculate — the method and its limits.
Sources
- USB Power Delivery specification: profiles are offered one at a time, and power above 3 A requires an electronically marked cable. Recorded in how we calculate and in
docs/calculation-methods.md. - Charger output labels and maker allocation tables, as printed by the manufacturer. This site does not republish model-specific tables, because they change between revisions of the same model.
Method reviewed 9 November 2026. No product data is published on this page; every figure comes from what you enter.