Phone/Device Charging Time Calculator
Calculate how long it takes to charge your device
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Phone/Device Charging Time Calculator helps you calculate how long it takes to charge your device — free, instant, in your browser. Drop Battery Capacity (mAh), Charger Wattage (W) and Battery Voltage (V) into Phone/Device Charging Time — the figure refreshes as you type. The answer from Phone/Device Charging Time arrives with its working attached. Phone/Device Charging Time replaces guesswork. No sign-up is needed for Phone/Device Charging Time. The math runs on your device. Phone/Device Charging Time is part of the Lifestyle collection on CalcProMaster, alongside phone/device charging time calculator, free online phone/device charging time calculator and more. The labels in Phone/Device Charging Time match the terms in its result. Phone/Device Charging Time is free, instant and local.
What the charging estimate is built on
Energy needed = battery capacity × percentage to fill × voltage. For the defaults — 5,000 mAh, 20% → 80% (that is 60% of the battery), 3.7 V — that is 11.1 Wh, and an 18 W charger at 85% efficiency delivers it in about 44 minutes.
The percentage you set matters as much as the charger. Filling the middle of a battery is fast; the last 20% is deliberately slowed by the charging circuit to protect the cells.
The two steps
Energy = mAh × (target% − current%) × voltage ÷ 1,000. Here: 5,000 × 0.60 × 3.7 ÷ 1,000 = 11.1 Wh.
Time = energy ÷ (watts × efficiency) × 60. Here: 11.1 ÷ (18 × 0.85) × 60 = 44 minutes.
The 85% figure stands in for conversion losses: the charger turns mains AC into DC, and the phone’s charge controller turns that into cell current. Both steps lose a little as heat, which is why the phone is warm while charging.
Worked variations
Same phone, 20 W charger: 11.1 ÷ 17 = 0.65 h, about 39 minutes.
Same phone, 5 W charger: 11.1 ÷ 4.25 = 2.6 h, about 157 minutes.
Same phone, 20% → 100%: 14.8 Wh, so about 58 minutes at 18 W.
That last line is the useful one. Jumping from 80% to 100% adds 20% of capacity but more than 20% of the time, because above roughly 80% the charger tapers its current.
Where this estimate is optimistic
- Charging curve. Power delivery is not constant: it is high in the middle of the range and falls away at both ends, so a long charge takes longer than the flat rate implies.
- Cable and port. A worn cable or a cheap adapter can halve the delivered wattage regardless of what the charger claims.
- Use while charging. A phone running navigation or a game is drawing power at the same time, so the battery fills more slowly.
- Heat. A hot battery is charged more slowly on purpose; a phone in the sun can take noticeably longer than the calculation.
Getting the inputs right
Battery capacity is in mAh as printed in the specification, not the “typical” marketing figure if both are listed. Voltage is the nominal cell voltage — 3.7 V for most lithium-ion phone packs, 3.8–3.85 V on newer chemistries. Charger wattage is the output on the adapter label, and fast charge only applies with a cable and phone that both support it.
Worked example
Everything below is the page’s own arithmetic: the defaults above, run through the same formula the calculator uses, so the figures can be reproduced by hand.
- Battery Capacity (mAh): 5000
- Charger Wattage (W): 18
- Battery Voltage (V): 3.7
- Current Battery %: 20
- Target Battery %: 80
The steps it follows:
- Step 1: Energy needed = 5000mAh × 60% × 3.7V / 1000 = 11.1 Wh
- Step 2: Time = 11.1Wh / (18W × 85%) = 44 min
The result is 44 minutes. The same run also reports: From 20% to 80% | 0.73 hours | 11.1 Wh needed. Change one input on the page and every number above recalculates from scratch — nothing is stored, so a second run with the same values returns the same figures.
Frequently Asked Questions
Why does 5,000 mAh from 20% to 80% take 44 minutes?
Filling 60% of a 5,000 mAh battery at 3.7 V needs 11.1 Wh. An 18 W charger delivers about 15.3 W after losses, and 11.1 ÷ 15.3 = 0.73 hours, or 44 minutes.
Why is the last 20% so much slower?
Because charging tapers. Above roughly 80% the phone deliberately reduces current to avoid damaging the cells, so the final stretch takes disproportionately long — full charges are much slower than the same energy in the middle range.
Does a 60 W charger charge my phone in a third of the time?
Only if the phone accepts that much. Most phones cap their own draw well below the charger’s rating, so the extra wattage sits unused; the calculation is only as good as the wattage the device actually takes.
What voltage should I enter?
The nominal cell voltage from the battery specification — 3.7 V for most lithium-ion phone packs. Entering the 5 V USB supply instead overstates the energy needed by about 35%.
Why is the real charge slower than the estimate?
The model assumes a constant rate, while a real charge tapers at both ends, and it ignores cable losses and any use during charging. Treat 44 minutes as the fast-case figure, not a promise.
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