Calculate the Rating, Then Verify the Source Data

The IATA 2026 Guidance Document for Lithium Batteries and Sodium Ion Batteries defines the Watt-hour rating of a lithium cell or battery as rated capacity in ampere-hours multiplied by nominal voltage. The same guidance explains that series connections increase voltage while capacity in Ah stays the same, whereas parallel connections increase Ah while voltage stays the same.

That gives two useful formulas:

Use these formulas to confirm supplied information, not to create a new rating for an unidentified product. If the calculated result and manufacturer-declared Wh do not agree, stop the review and resolve the source data before requesting a booking.

What a Watt-Hour Rating Means for Battery Shipping

A Watt-hour is a unit of energy. For transport purposes, the relevant figure is the nominal energy of the specific lithium-ion cell or battery design. It combines two manufacturer-declared values:

• Nominal voltage (V): the approximate voltage used to identify the cell or battery.
• Rated capacity (Ah or mAh): the capacity established under the manufacturer's specified load, temperature and voltage cut-off conditions.

Watt-hours are not the same as watts. Watts describe power at a point in time; Watt-hours describe an amount of energy. Ampere-hours are not Watt-hours either, because the same Ah capacity can represent different energy at different voltages.

For example, a 5 Ah battery at 3.7 V is 18.5 Wh, while a 5 Ah battery at 11.1 V is 55.5 Wh. The capacity in Ah is the same, but the energy rating is not.

The Wh relationship applies to lithium-ion cells and batteries, including lithium-polymer designs within the lithium-ion family. Lithium-metal transport provisions use lithium content or aggregate lithium content instead of treating Wh as the equivalent decision measure. Use the separate UN3090 vs UN3091 guide when the battery contains lithium metal rather than rechargeable lithium-ion chemistry.

The UN Manual of Tests and Criteria, Revision 8 provides the current public UN testing context for cell and battery design types. A calculation does not prove that the design passed UN 38.3, and it does not replace the manufacturer's declared information.

Use the Correct Voltage and Capacity Values

Most serious Wh errors begin before the multiplication. The numbers may be genuine but belong to different electrical functions, different physical levels or different model variants.

Use nominal voltage

Use the nominal voltage declared for the battery model. Do not substitute:

• maximum charge voltage;
• a charger's input or output voltage;
• a power bank's USB output voltage;
• an equipment operating voltage that does not describe the battery;
• the voltage of one cell when the record is for an assembled pack; or
• a voltage copied from a similar product.

A lithium-ion cell marketed as “3.7 V” may show a higher maximum charge voltage elsewhere in its technical data. The higher value is not the nominal voltage for the Wh relationship.

Use rated capacity

Use rated capacity for the exact model, expressed in Ah or mAh. Do not replace it with:

• the battery's current measured remaining capacity;
• the percentage state of charge;
• a state-of-health estimate for a used battery;
• a product runtime claim;
• the charger's current rating; or
• the combined quantity of batteries in the consignment.

The IATA guidance distinguishes rated capacity from state of charge. Rated capacity is a characteristic declared for the cell or battery; SoC is the percentage of that rated capacity stored at a particular time. Reducing a battery to 30% SoC does not turn a 100 Wh design into a 30 Wh battery.

Match the exact model

Record the manufacturer, full model number and relevant suffix before calculating. A shared product name is not enough when variants use different cell suppliers, voltages or capacities.

Preferred evidence includes:

1. the marking on the battery case;
2. the manufacturer's technical specification for the exact model;
3. the matching UN 38.3 test summary;
4. supporting SDS/MSDS information; and
5. the battery details stated in the product and shipment records.

The documents do not all perform the same job, but their identity fields should describe the same battery.

How to Calculate Wh from Ah or mAh

Use this eight-step review for one exact cell or battery model.

1. Identify the article. Confirm whether the rating is for a cell, an assembled battery, a battery pack, a power bank or a battery installed in equipment.
2. Record the manufacturer and model. Do not calculate from an untraceable label fragment.
3. Find nominal voltage. Record the value and its V unit.
4. Find rated capacity. Record the number and confirm whether it is Ah or mAh.
5. Convert mAh when necessary. Divide mAh by 1,000 to obtain Ah.
6. Multiply without premature rounding. Keep enough precision to see whether the result is near a regulatory decision point.
7. Label the physical level. State whether the answer belongs to one cell or one complete battery.
8. Reconcile the answer. Compare it with the declared Wh and the exact model shown in the technical and transport records.

Example 1: capacity stated in Ah

A lithium-ion cell is marked 3.7 V and 2.6 Ah.

3.7 V × 2.6 Ah = 9.62 Wh

The calculated cell rating is 9.62 Wh. This does not state the rating of a multi-cell battery built from that cell.

Example 2: capacity stated in mAh

A power bank's internal battery data states 3.7 V and 5,000 mAh.

First convert the capacity:

5,000 mAh ÷ 1,000 = 5 Ah

Then calculate energy:

3.7 V × 5 Ah = 18.5 Wh

The 3.7 V internal battery value is used here. A 5 V USB output does not make this battery 25 Wh.

Example 3: assembled battery pack

A battery pack specification states 11.1 V and 4.4 Ah.

11.1 V × 4.4 Ah = 48.84 Wh

Confirm that both values describe the complete pack and that the model matches the label and test summary.

Example 4: a value just above 100 Wh

A battery pack is stated as 14.8 V and 6,800 mAh.

14.8 V × 6,800 mAh ÷ 1,000 = 100.64 Wh

Do not round 100.64 Wh down to 100 Wh to fit a threshold. Ask the manufacturer to confirm the declared rating and apply the relevant current provision to the actual value.

These examples illustrate arithmetic only. They are not shipment classifications, approvals or packing instructions.

Cell, Battery and Battery-Pack Calculations Are Not Interchangeable

The physical level matters. Under the terminology summarized by IATA, a cell is one encased electrochemical unit. Two or more electrically connected cells fitted with the devices needed for use are treated as a battery. Products called “battery packs,” “modules” or “battery assemblies” may therefore be batteries for transport purposes.

A supplier may provide all of the following values for the same product family:

• Wh per cell;
• Wh per assembled module;
• Wh per battery pack;
• total nominal energy for several batteries in one system; and
• total Wh for all batteries in a shipment.

Those values answer different questions. Do not place the shipment total in a field asking for the rating of each battery. Do not place one cell's rating in a field asking for the complete battery rating.

For a simple pack made from identical cells, cell arithmetic can help detect an inconsistency. It should not be used to override the manufacturer's pack rating when the internal configuration, protection electronics, rated capacity or applicable model is uncertain.

Worked Series and Parallel Examples

Assume an identical lithium-ion cell rated at 3.7 V and 2.6 Ah. Each cell is:

3.7 × 2.6 = 9.62 Wh

The following examples are idealized electrical cross-checks:

In a series connection, the nominal voltages add while Ah remains the same. In a parallel connection, Ah adds while nominal voltage remains the same. The 3S and 3P examples have the same theoretical energy because both contain three identical 9.62 Wh cells, even though their voltage and Ah presentation differs.

Real shipment records should use the pack manufacturer's declared values for the exact model. If the label says 54 Wh while an assumed cell arrangement suggests 57.72 Wh, do not “correct” the label from the outside. Check whether the assumed cells, rated capacity, configuration or model are wrong and obtain responsible manufacturer clarification.

How to Calculate a Power Bank’s Watt-Hours

Power banks frequently show a large mAh figure and several USB output voltages. That combination creates avoidable mistakes.

The IATA 2026 guidance treats a power bank primarily designed to supply power to another device as a battery, not as a battery contained in equipment. For the Wh calculation, use the nominal voltage and rated capacity of the internal battery—not the output voltage used to charge a phone or laptop.

For example:

• internal battery: 3.7 V, 20,000 mAh;
• USB output options: 5 V, 9 V, 12 V.

The basic internal-battery calculation is:

3.7 × 20,000 ÷ 1,000 = 74 Wh

Using 5 × 20,000 ÷ 1,000 would produce 100 Wh, but it combines an output voltage with internal battery capacity and does not describe the battery rating.

Some power banks use multi-cell arrangements, and promotional capacity claims may omit the exact internal battery model or use a different reference basis. Prefer the Wh printed by the responsible manufacturer and verify it against model-specific technical information. If the internal data cannot be traced, do not infer transport eligibility from marketing copy.

For commercial routing, quantity, packaging and destination questions, use the dedicated guide to shipping power banks from China.

What the 20 Wh and 100 Wh Decision Points Do—and Do Not Mean

The IATA 2026 lithium-ion classification flowchart distinguishes cells at 20 Wh and batteries at 100 Wh within specific air packing-instruction pathways. These figures are important decision points, but they are not universal permission to ship.

A full air review may still depend on:

• whether the article is a cell or battery;
• UN3480 or UN3481 configuration;
• the applicable packing instruction and section;
• state of charge;
• number of cells or batteries;
• net battery weight and package count;
• package construction and test conditions;
• marks, labels and documentation;
• origin, destination and transit States;
• State and operator variations; and
• airline, airport and handling acceptance.

Other modes and jurisdictions have their own current provisions. A lithium-ion battery below 100 Wh is not automatically non-dangerous, unrestricted or acceptable to every carrier. A battery above 100 Wh is not automatically forbidden from all transport. It moves into a different decision path that must be checked for the actual mode and shipment.

Do not manipulate precision to reach a preferred answer. If a calculation gives 100.64 Wh, retain that result and obtain the manufacturer-declared rating. If a label states 100 Wh but the matching nominal voltage and capacity calculate to a materially different value, treat it as an inconsistency rather than choosing whichever number is more convenient.

Compare the Result with the Battery Label and Transport Records

Arithmetic becomes useful when it is part of a model-matching review.

The IATA guidance's test-summary section includes model numbers, physical description, mass and either Watt-hour rating or lithium content among the design-description fields. This is why a generic test report for a different model cannot resolve a Wh question.

Use the UN 38.3 test summary guide for the complete record check. Use the lithium battery SDS/MSDS guide to understand what an SDS can support and what it cannot establish.

Common Watt-Hour Calculation Errors

1. Multiplying volts by mAh without dividing by 1,000

3.7 V × 5,000 mAh is not 18,500 Wh. Convert 5,000 mAh to 5 Ah first; the result is 18.5 Wh.

2. Using maximum charge voltage

Maximum charge voltage describes a different operating point. Use the model's nominal voltage for the Wh relationship.

3. Using a power bank's USB output voltage

The output may be 5 V, 9 V or 12 V while the internal battery has another nominal voltage. Use model-specific internal battery data.

4. Confusing one cell with the complete battery

Identify whether each figure describes a cell, module or complete pack before multiplying.

5. Multiplying by shipment quantity

Ten identical 48.84 Wh batteries do not each become 488.4 Wh. The shipment has ten batteries, each rated 48.84 Wh. Quantity and total net battery weight are separate fields.

6. Using remaining capacity or SoC

A partially discharged 100 Wh battery remains a 100 Wh rated battery. State of charge is a separate transport input.

7. Mixing model data

Voltage from one model and capacity from another can produce mathematically correct but operationally meaningless output.

8. Rounding down to fit a threshold

Do not round 100.64 Wh to 100 Wh. Preserve the result and resolve the declared rating with the manufacturer.

9. Treating Wh as evidence of UN 38.3 testing

Wh is one design fact. It does not show which tests were conducted or whether the design passed.

10. Assuming “below 100 Wh” guarantees acceptance

Configuration, quantity, packaging, documentation, SoC, route and operator rules still apply.

What Watt-Hours Cannot Decide

Watt-hours can help describe a lithium-ion cell or battery, but the value cannot independently decide:

• whether the cargo is UN3480 or UN3481;
• whether a UN3481 battery is packed with or contained in equipment;
• whether a lithium-metal battery is UN3090 or UN3091;
• whether the exact design passed UN 38.3;
• which packaging, marks, labels or transport documents apply;
• the required state of charge;
• whether a prototype approval pathway is relevant;
• whether a used battery is a product or waste;
• whether a battery is damaged, defective or recalled;
• whether air, sea, courier, road or rail transport is available; or
• whether a carrier, port, airport, customs authority or destination party will accept the shipment.

For lithium-ion configuration, use UN3480 vs UN3481. For physical preparation, use the lithium battery packaging review, lithium battery marks and labels guide and lithium battery shipping documents checklist. For the 2026 air-capacity question, keep Wh separate from the state-of-charge rules for air shipping.

Pre-Enquiry Watt-Hour Verification Checklist

Before sending a battery shipment for route review, confirm that:

• The responsible battery and product manufacturers are identified.
• The complete battery and product model numbers are recorded.
• The chemistry is known.
• Cell, assembled battery, module, pack and equipment levels are not confused.
• Nominal voltage and rated capacity belong to the same exact model.
• Capacity units are clearly stated as Ah or mAh.
• The mAh-to-Ah conversion and Wh multiplication have been checked.
• The result has not been rounded downward to fit a threshold.
• Declared Wh agrees across the battery case, specification and UN 38.3 test summary.
• The number of batteries per product, package and consignment is stated separately.
• Configuration, condition, SoC where relevant, packaging and route data are available.
• Any mismatch has been returned to the responsible manufacturer or document issuer.
• No classification or booking promise has been made from Wh alone.