How Big Of A Power Bank Do I Need? | Smart Sizing

Choosing the right portable charger isn’t about chasing the biggest number on the box. The goal is steady power when you need it, without lugging around a brick. This guide shows a simple way to size a pack for phones, tablets, laptops, and travel rules. You’ll get a short formula, a quick chooser table, and tips that avoid common mistakes like buying by mAh alone or ignoring wattage.

Quick Picks By Use Case

The table below gives fast matches for common scenarios. It balances pocketability, real-world efficiency losses, and how many full phone charges most people actually want.

Use Case	Capacity Target (Wh / mAh@3.7V)	Phone Recharges*
Daily top-ups for a compact phone	10 Wh / ~2700 mAh	~1
All-day city daytrip (maps + photos)	20 Wh / ~5400 mAh	~2
Weekend getaway, two phones	35–40 Wh / ~9500–10800 mAh	~3–4
Tablet heavy use	45–60 Wh / ~12,000–16,000 mAh	Phone 3–5 + tablet top-ups
Ultrabook emergency top-off	70–90 Wh / ~19,000–24,000 mAh	~20–40% of a thin-and-light
USB-C laptop working session	90–100 Wh / ~24,000–27,000 mAh	~1–3 hrs at 45–65 W

*Phone recharges are ballpark figures; fast charging, screen time, and wireless charging change outcomes.

How To Size A Power Bank The Right Way

Step 1: Find Your Device’s Battery In Wh

Many spec sheets list batteries in milliamp-hours. Energy is measured in watt-hours. To estimate watt-hours, multiply the listed mAh by the battery’s nominal voltage and divide by 1000. For most phone packs, 3.7 V is a sensible default when the exact voltage isn’t printed.

Handy Rule

Wh ≈ (mAh × 3.7) ÷ 1000  •  A 5000 mAh phone is ~18.5 Wh.

Step 2: Choose 2–3× Your Largest Daily Load

Pick a bank with two to three times the watt-hours of your biggest device you plan to refill that day. That covers conversion losses and gives wiggle room for GPS, hotspot use, or camera bursts. If you only need a safety net for a single phone, 2× feels light and pocketable. If you share power with family or run video a lot, lean closer to 3×.

Step 3: Match Output Wattage To Your Devices

Capacity keeps you going; output wattage decides how fast you charge. Look for USB-C with Power Delivery. Phones usually sip 18–30 W, tablets 20–45 W, and many thin laptops need 45–65 W, while larger USB-C notebooks may ask for 100 W.

Step 4: Keep It Flight-Legal

For air travel, stick to packs marked at or below 100 Wh to avoid approvals. Packs between 101 and 160 Wh often need airline sign-off, and anything larger is generally not allowed for passengers. Power banks count as spare batteries and stay in hand baggage only.

What Size Power Bank Do You Need For Flights And Daily Carry?

Size isn’t only about capacity. Weight, port layout, and charging standards matter just as much for day-to-day use. A slim 10–20 Wh pocket bank covers late nights and rides home. A 35–60 Wh unit works for content creation days, a road trip, or two phones. For laptop flexibility, a 90–100 Wh bank with 65–100 W USB-C PD turns a café into a temporary desk.

Real-World Sizing Examples

Modern Phones

Many current flagships sit near 3300–5000 mAh. Using the 3.7 V estimate, that’s ~12–19 Wh. A 20 Wh bank gives one to two full refills for most phones, while a 40 Wh unit handles a busy weekend without wall power.

Tablets

Mid-size tablets often range from 7000–10,000 mAh (≈26–37 Wh). A 45–60 Wh bank can raise a tablet from low to comfortable while still topping up a phone.

USB-C Laptops

Thin-and-lights commonly draw 45–65 W when charging. A 90–100 Wh bank rated for at least 65 W output can stretch work time by an hour or three, depending on your screen brightness and workload. Gaming machines generally draw more than portable packs can supply.

Make Sense Of mAh, Wh, And Fast-Charge Labels

mAh vs Wh

mAh describes charge at a given voltage; Wh expresses stored energy. Two packs with the same mAh can carry different energy if their voltages differ. When shopping, treat Wh as the apples-to-apples number.

USB-C PD, PPS, And Wattage

USB-C Power Delivery lets chargers and devices agree on a safe voltage and current. Common phone profiles include 9 V × 2 A (18 W) and 12 V × 2.5 A (30 W). Many tablets and ultrabooks use 20 V × 3.25 A (65 W) or 20 V × 5 A (100 W). PPS lets voltage adjust in small steps for cooler, steadier charging on compatible phones.

Packing For A Flight

Airlines and security agencies set limits by watt-hours. Keep these two points front and center: spare lithium batteries go in carry-on only, and a pack marked 100 Wh or less sails through most counters without extra paperwork. Between 101 and 160 Wh, many carriers allow up to two units with approval. Over 160 Wh is typically cargo-only territory.

Battery Rating	Carry-On	Checked Bag
≤ 100 Wh	Allowed (no approval)	Not allowed for spares
101–160 Wh	Usually allowed with airline approval (often max two)	Not allowed for spares
> 160 Wh	Not allowed for passengers	Not allowed

Labeling And Conversions

Most modern packs print the Wh on the case. If you only see mAh, use the quick formula up top. For travel sizing, the Wh figure is what matters at the counter.

Buying Tips That Save Hassle

Prefer USB-C Input And Output

USB-C in and out makes a small pack easier to refill and share across devices. Look for a model that can charge and be charged via USB-C.

Match The Cable To The Job

A 100 W bank still crawls if you use a slow cable. For anything over 60 W, grab an e-marked USB-C cable rated for 100 W.

Watch For Efficiency Claims

Marketing numbers assume ideal lab cases. Heat, conversion, and standby drain eat into real capacity. A 20 Wh bank rarely yields a full 20 Wh at the USB port.

Wireless Charging Costs Energy

Magnetic wireless banks lose more energy than a cable. If you care about every last percent, plug in.

Features Worth Paying For

• Pass-through charging that lets the bank power a device while it charges.
• Clear display of remaining Wh or a simple percentage that’s reliable.
• Multiple USB-C ports for a laptop and phone at the same time.
• Low-current mode for earbuds and watches.

Safety And Care

Retire any pack that swells, smells odd, or runs hot at idle. Keep terminals covered when the bank rides in a bag with keys or coins. On a plane, keep the pack within reach and avoid charging it while wedged into a seat pocket.

Two Simple Paths To The Right Size

The Quick Path

Pick a bank that’s 2–3× your biggest device in Wh, check that the USB-C wattage matches that device, and keep the label at 100 Wh or under if you travel.

The Precise Path

1. Look up your device’s mAh and convert to Wh with the 3.7 V rule.
2. Estimate how many times you want to refill that device between wall charges.
3. Multiply the device Wh by that number, then add a buffer of 25–40% for losses and mixed use.
4. Match the bank’s listed Wh and output wattage to that target.

Common Combos That Work Well

• Pocket carry: 20 Wh bank with 20–30 W PD for phones and small earbuds.
• Creator kit: 40–60 Wh bank with 30–45 W PD for phone, action cam, and tablet.
• Travel office: 90–100 Wh bank with 65–100 W PD and two USB-C ports for an ultrabook and phone.

Linked sources for rules and definitions: the TSA lithium battery page and IATA’s passenger lithium battery guidance.