Battery Capacity Converter — mAh to Wh & Ah

mAh and Ah measure electric charge; Wh measures energy. The relationships are 1 Ah = 1,000 mAh, Wh = Ah × V, and 1 Wh = 3,600 J. Enter mAh, Ah, Wh or mWh to see results in all four units plus kWh and joules.

For example, 20,000 mAh at a nominal 3.7 V equals 20 Ah or 74 Wh. Use the voltage corresponding to the stated capacity. Do not multiply a cell-rated mAh figure by the USB output voltage of 5 V. Battery chemistry and pack configuration affect nominal voltage, so check the product specifications instead of assuming the default applies.

No voltage is needed to convert between mAh and Ah, or from Wh and mWh to other energy units. Missing voltage only prevents conversions between charge and energy.

Rated energy = rated mAh ÷ 1,000 × cell voltage. Output energy = rated energy × efficiency. Capacity at the output voltage = output Wh ÷ output voltage × 1,000. Enter efficiency as a percentage: the default 85% is a sample assumption, not a universal product specification.

A 20,000 mAh, 3.7 V battery at 85% efficiency supplies an estimated 62.9 Wh, equivalent to 12,580 mAh at 5 V. At 100% efficiency it would supply 74 Wh or 14,800 mAh at 5 V. The lower mAh figure alone is not evidence of energy loss: voltage also changed.

Estimated full charges = output Wh ÷ the device battery's rated Wh. A 3,000 mAh battery at 3.85 V is 11.55 Wh, giving 62.9 ÷ 11.55 ≈ 5.45 charges. This excludes charging losses inside the device, power used during charging and aging. Changing output voltage alone does not change Wh or charge count when efficiency is unchanged.

This is an ideal model with identical cells connected uniformly. Series count S adds voltage; parallel count P adds amp-hours. Pack Wh = cell mAh ÷ 1,000 × cell voltage × S × P. Six 3.7 V, 3,000 mAh cells in a 3S2P pack give 11.1 V, 6,000 mAh and 66.6 Wh. With the same total cell count, ideal energy is independent of the series/parallel arrangement.

The diagram illustrates the arrangement. It is not a wiring or assembly guide and does not assess protection circuits, current ratings, compatibility or safety.

Choose a main result unit to highlight the conversion you need. Changing a unit keeps the entered number and interprets it in the new unit. “Reverse using result” instead places the calculated result into the input and swaps the units. The expandable capacity table uses your selected nominal voltage.

“Copy conditions and results” includes the inputs, units, results and assumptions. If automatic copying fails or is waiting for browser permission, use “Show manual copy text” to select and copy the current calculation. Each mode retains its inputs. Clear and reset affect only the current mode.

Use ASCII numbers or scientific notation, up to 32 characters per input. Capacity must be nonnegative; voltages, device battery capacity and cell capacity must be positive. Efficiency accepts 0–100%. Series and parallel counts must each be integers from 1 to 1,000,000.

Inputs are interpreted as floating-point numbers. Results show up to about 12 significant digits, with scientific notation for very large or tiny values. If a result is too large or a nonzero value cannot be represented, it shows “Out of numeric range”; other valid results remain available. Calculations run in your browser, while site-wide analytics and advertising use separate network requests.

Rated Wh is useful for comparing stored energy, but it does not guarantee how much energy a product will deliver. Load, temperature, aging, circuitry and charge level affect actual performance. A low charge count alone does not establish whether a product is faulty.

This tool does not determine whether a battery is allowed on a flight. Check the battery label and product specifications, then consult the current guidance from your airline and relevant authorities.