Measure across the battery, and its thickness if you can, to find the coin or button cell code of that size.
Measure across the flat face. Add the thickness after an x, such as 20 x 3.2, to tell same-width cells apart.
Your battery is most likely
How to measure it
Calipers give the best reading. Measure straight across the flat face for the width, then from face to face for the thickness. A ruler can find the width to the nearest half millimeter, which is enough to tell a 20 mm coin cell from a 23 mm one, but too coarse for thickness.
Thicknessjaws on both flat faces
For the thickness, close the jaws on the two flat faces. For the width, measure straight across a face.
The makers allow a little under the printed size. Energizer’s CR2032 drawing allows 19.7 to 20 mm across, and Renata’s 377 sheet 6.65 to 6.8 mm, so a cell that measures a hair small is still that cell.
Cells that share a width
Width alone often isn’t enough. Four coin cells in our list are 20 mm across, the CR2012 (1.2 mm thick), CR2016 (1.6 mm thick), CR2025 (2.5 mm thick) and CR2032 (3.2 mm thick). Six sizes of button cell are 11.6 mm across, from 1.6 to 5.4 mm thick.
One size can come in two chemistries. An alkaline LR44 and a silver oxide 357 are both 11.6 x 5.4 mm; an alkaline LR41 and a silver oxide 392 both 7.9 x 3.6 mm. The device’s manual says which it takes.
Coin cell or button cell
Coin cells in our list are lithium, 3 V, and 10 to 24.5 mm across. Their codes start with CR.
Button cells are 4.8 to 11.6 mm across and thicker for their width. Alkaline ones (LR codes) are 1.5 V; silver oxide watch cells (SR codes and three-digit numbers) are 1.55 V.
If anyone may have swallowed a coin or button battery, don’t delay: call the 24-hour National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222.
Common questions
Is a 20 mm coin battery always a CR2032?
No. Energizer makes four 20 mm lithium coin cells in our list, the CR2012, CR2016, CR2025 and CR2032, which are 1.2, 1.6, 2.5 and 3.2 mm thick.
How accurate does my measurement need to be?
Energizer's and Renata's drawings allow up to 0.35 mm under the printed width, so measure to the tenth of a millimeter with calipers where you can.
Can I measure in inches?
Yes. Type the size in inches: 0.787 in is 20 mm, the width of the four 20 mm coin cells.
Sizes and their tolerances come from Energizer’s coin and alkaline button datasheets and Renata’s product pages and data sheets; the swallowing line from the National Capital Poison Center. Checked against published data from Energizer, Renata, National Capital Poison Center and GP Batteries.
See all 26 sources
National Capital Poison Center (poison.org), Battery ingestion: National Battery Ingestion Hotline
Renata, silver oxide battery product pages (technical data and cross reference guide)
Renata, lithium coin battery product pages (technical data and cross reference guide)
GP Batteries, alkaline button cell and lithium coin product pages (specification and equivalent models)
Renata, 377 (SR626SW) silver oxide technical data sheet (PDF)
Renata, 392 (SR736W, SR41) silver oxide technical data sheet (PDF)
Renata, 390 (SR1130SW) silver oxide technical data sheet (PDF)
Battery sizes come from battery makers' datasheets and device makers' own manuals and help pages. Check your device's manual or the old battery before you buy. If anyone may have swallowed a battery, call the National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222 straight away.
