IPS Calculator

Enter total load, hours and battery count. For example, 400W for 4 hours needs 500 VA and a 133 Ah battery.

Total load (watts)

Add up: fan 100 + light 20 + TV 100 = 220W

Backup wanted (hours)

Batteries (12V each)

You need

500 VA · 133.3 Ah

Total energy: 1,600 Wh
IPS size: 500 VA
Per battery (12V): 133.3 Ah

You need about a 500 VA IPS with 1 × 133.3 Ah batteries (12V).

Backup shrinks as batteries age. Buy ~20% bigger than the math says.

How this was calculated

Energy = 400 × 4 = 1,600 Wh; IPS = 400 ÷ 0.8 ≈ 500; battery = 1,600 ÷ 12 = 133.3 Ah

Calculated at: https://xn--d6bxcvd.xn--54b7fta0cc/en/ips-calculator/

How to use

Add up all appliance watts for the total load.
Enter backup hours wanted.
Enter how many 12V batteries to use.

IPS formulas

What	Formula	Example
Energy	Load × hours	400 × 4 = 1,600 Wh
VA	Load ÷ 0.8	400 ÷ 0.8 = 500
Battery	Energy ÷ 12 ÷ count	1,600 ÷ 12 = 133 Ah

Examples

2 fans + 3 lights + TV: 200+60+100 = 360W for 3h — 450 VA, 90 Ah.

Office: 800W, 2h, 2 batteries — 1,000 VA, 66.7 Ah each.

More: what to check when buying

Sine-wave IPS suits fans and lights; pick one with UPS mode for computers. Tubular batteries last longer. Match charging current to ~10% of Ah — about a 13A charger for 133 Ah.

Frequently asked questions

How is IPS size found?

VA = load ÷ 0.8 (power factor). 400W needs 500 VA, rounded up to multiples of 50.

What Ah battery do I need?

Ah = load × hours ÷ 12 ÷ battery count. 400W × 4h = 1,600Wh; one battery means 133 Ah.

What if I use 2 batteries?

Each carries half — 66.5 Ah each above. Let the technician wire for your system voltage.

Can it run a fridge or motor?

They draw 3–5× at startup. For heavy loads consider solar or a generator instead of IPS.

What if backup drops?

Check water/charge; replace at 3–4 years old. Less load also stretches backup.

Also searched as

ips battery size · backup hours calculator