Cell Size Calculator
Choose the cell type and enter the pack voltage, capacity and load current. The calculator gives the series and parallel count, the total cells, the energy and the weight.
- Cells needed
- Layout
- Energy
Use nominal voltage, not full charge voltage.
Series = voltage ÷ cell volts, parallel = capacity ÷ cell Ah. A 48 V, 20 Ah pack from 21700 cells needs 14 in series and 4 in parallel: 56 cells, 1,008 Wh and about 3.9 kg of cells.
Pack layout chart
21700 cells. Search for a voltage.
| Pack | Series | 10 Ah | 20 Ah |
|---|---|---|---|
| 12 V | 4 | 8 | 16 |
| 24 V | 7 | 14 | 28 |
| 36 V | 10 | 20 | 40 |
| 48 V | 14 | 28 | 56 |
| 52 V | 15 | 30 | 60 |
| 60 V | 17 | 34 | 68 |
| 72 V | 20 | 40 | 80 |
Cells.
Voltage and cells
18650 cells, 10 Ah. Slide the voltage.
Cells are drawn in rows.
How to size a battery pack
Pack to cells. Step through it.
Voltage
Pack nominal.
Spot weld nickel strip, never solder cells directly.
18650, 21700 or LiFePO4
Cells. Compare them.
Classic.
Bigger.
Safe.
LiFePO4 is safer and lasts longer, but is heavier.
Before you build
Pack checks. Tick each item.
Tick each item as you go.
Use cells from one batch with matched capacity.
What you get
Cell sizing. Each tile explains one result.
Count.
S and P.
Wh.
kg.
Rating.
Every cell group in series must have the same capacity.
Frequently Asked Questions
No question matches that search.
How many cells do I need for a forty eight volt battery?
Thirteen or fourteen lithium ion cells in series, or sixteen LiFePO4 cells.
What does thirteen S four P mean?
Thirteen cells in series and four in parallel.
How do I work out battery capacity?
Multiply the cell capacity by the number of cells in parallel.
Are lithium iron phosphate cells safer?
Yes. They are much less likely to catch fire.
Do I need a BMS?
Yes. It protects every cell from over charge and over discharge.
How heavy is an e-bike battery?
Usually three to five kilograms for about five hundred to one thousand Wh.
A pack you can build
Count the cells first and the battery has the voltage and range you need.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.