Hobbies · Model railroading · DCC
DCC booster calculator.
Enter how many locomotives run at once, how many sit idle and how many lit cars you have, and the calculator adds the current using Digitrax's planning figures. Example: ten HO locomotives running at 650 mA each draw 6.5 amps, which is 130% of a 5 amp booster but 81% of an 8 amp one.
Your numbers
Result
Working out the result.
How the current is calculated
The figures come from Digitrax's Tech Support Depot article KB342, Powering your Digitrax Railroad: An Example, dated 18 January 2012 and read 26 October 2026. Digitrax says to estimate: each locomotive draws at least 5 mA for its decoder; LED lighting adds 15 mA typically and a conventional bulb 50 mA; a typical HO locomotive draws 600 mA in operation and an N-scale one 300 mA; to get into the ballpark, 650 mA per HO locomotive and 350 mA per N locomotive. Passenger cars with internal bulbs draw 50 mA each, and with LEDs 15 mA each. The article says the number will be higher for a locomotive with sound but gives no figure, so this page asks for yours.
The calculator multiplies the running locomotives by 650 or 350 mA, adds your own sound extra, then adds each idle locomotive at 5 mA plus its lighting and each lit car at 15 or 50 mA. The total in amps is compared with the 5 amp and 8 amp boosters Digitrax mentions in the same article, giving the load on one booster and the number of boosters needed to carry the total. The bus wire the article assumes is 12 gauge, with a drop of about half a volt over 50 feet.
These are planning numbers from a manufacturer's help article, 14 years old. Digitrax itself says you have to estimate. Measure your own locomotives with a meter if the answer matters.
Worked examples with real numbers
- The Digitrax example: ten HO locomotives. 10 × 650 mA = 6,500 mA, 6.5 amps. One 5 amp booster would be at 130%; one 8 amp booster at 81%; or two 5 amp boosters would share it.
- A smaller N layout. Six running N locomotives at 350 mA is 2,100 mA. Twelve idle locomotives with LED lights at 5 + 15 = 20 mA each is 240 mA. Twenty LED passenger cars at 15 mA is 300 mA. The total is 2,640 mA, 2.64 amps, 53% of a 5 amp booster.
- Bulb versus LED cars. Twenty passenger cars draw 1,000 mA with bulbs and 300 mA with LEDs, a difference of 0.7 amp.
What this calculator leaves out
It does not know your decoders' stall current, your short-circuit trip settings, your power supply, or your wiring. It does not recommend a number of power districts for your plan; it only repeats Digitrax's own suggestion. Other makers' boosters have their own ratings. Check yours.
Frequently asked questions
How many amps does an HO locomotive draw?
Digitrax's planning figure is 650 mA per HO locomotive and 350 mA per N locomotive, including the decoder and lights. Sound locomotives draw more. The article calls these ballpark figures.
How many boosters do I need for ten HO locomotives?
Ten locomotives at 650 mA is 6.5 amps, over one 5 amp booster. Use one 8 amp booster or two 5 amp boosters.
Do idle locomotives use power?
Yes. Digitrax says each decoder draws at least 5 mA, plus 15 mA for LED lights or 50 mA for a bulb.
How much current do lit passenger cars draw?
Digitrax gives 50 mA per car with internal bulbs and 15 mA per car with internal LEDs.
Why does the page not include sound locomotive current?
Digitrax says sound locomotives draw higher current but gives no number. The page lets you enter your own measured extra.
Are these numbers exact?
No. Digitrax says to estimate, and the article is dated 2012. Measure real locomotives with a meter if the figure matters for your layout.
Sources
Retrieved
- Digitrax KB342: Powering your Digitrax Railroad, An Example (article dated 18 January 2012) — per-locomotive and per-car current, the 5 amp and 8 amp boosters, the 12 gauge bus figure (read 2026-10-26)
Manufacturer planning figures
Not affiliated with Digitrax. The article was read on 26 October 2026. These are estimates, not a guarantee that a booster will carry a layout. Nothing you type is sent or stored.