Charge Time Calculator

Ever wondered how long it’ll take to fully charge your phone, tablet, or any other device? This calculator gives you a quick estimate. Just enter your battery capacity (mAh) and your charger’s power (W or mA), and you’ll know how much time you need to get from empty to full. Perfect for planning when you’re on the go or trying to figure out if your charger is fast enough.

How to Calculate Charging Time

The charging time for a device depends on two main things:

1. Battery capacity (measured in milliamp-hours, mAh, or watt-hours, Wh).
2. Charger output (measured in milliamps, mA, or watts, W).

📐 Formula 1: Using mAh and mA

Charging Time (in hours) = Battery Capacity (mAh) ÷ Charger Output (mA)

Example:
A 5,000 mAh battery with a 2,000 mA charger →
5,000 ÷ 2,000 = 2.5 hours (plus some extra for inefficiency).

📐 Formula 2: Using Wh and W

Charging Time (in hours) = Battery Capacity (Wh) ÷ Charger Power (W)

To get watt-hours (Wh) from milliamp-hours (mAh), use:
Battery Capacity (Wh) = (Battery Capacity (mAh) × Battery Voltage (V)) ÷ 1000

Example:
A 5,000 mAh battery at 3.7 volts → (5000 × 3.7) ÷ 1000 = 18.5 Wh.
With a 20W charger → 18.5 ÷ 20 = about 0.9 hours (plus inefficiency).

What Affects Charging Speed?

1. Battery Size – Bigger batteries take longer.
2. Charger Power – Higher wattage = faster charging.
3. Fast-Charging Tech – USB-C PD, Quick Charge, VOOC, and others cut time dramatically.
4. Battery Health – Older batteries charge slower.
5. Charging Curve – Phones often charge very fast from 0–80%, then slow down to protect battery health.

Real-World Examples

• A 5,000 mAh phone with a standard 10W charger takes about 3–3.5 hours.
• The same phone with a 25W charger takes around 1.5 hours.
• An iPad Pro (10,758 mAh) can take 3–4 hours on its included charger, but much less with a higher watt charger.

Fun Facts About Charging

• The first mobile phone, the Motorola DynaTAC 8000X (1983), took 10 hours to charge for only 30 minutes of talk time!
• Wireless charging is slower, but improving—some pads now reach 50W.
• Xiaomi’s 120W charging can fill a 4,500 mAh battery in under 20 minutes.
• Many modern phones use “smart charging” at night, pausing at 80% and finishing right before you wake up to protect battery life.

Frequently Asked Questions

Q: Is it bad to charge my phone overnight?
A: No, modern phones stop charging at 100% and use trickle charging. But heat buildup can still reduce battery health, so smart charging is better.

Q: Does fast charging damage the battery?
A: Fast charging produces more heat, which can shorten long-term health slightly. But most phones manage this with smart charging curves.

Q: Why does my phone charge slow after 80%?
A: This is intentional. Charging slows down near full to reduce stress on the battery and prevent overheating.

Q: Can I use any charger with my phone?
A: As long as the charger meets the voltage/amperage your device supports, yes. But low-quality chargers can be unsafe and reduce battery life.

Key Takeaway

To estimate charging time:

• Use Formula 1 if you know mAh and mA.
• Use Formula 2 if you know Wh and W.

Always add about 10–20% extra time for real-world charging because no system is 100% efficient.

With the right charger and cable, you can cut hours off your charging time and keep your devices ready when you need them most.