Battery Discharge Rate (C-Rate) Calculator

Convert between C-rate, discharge current, and runtime for any pack. Enter capacity in Ah or mAh, pick what to solve for, and the tool applies I = C-rate x capacity, C-rate = I / capacity, and runtime = 1 / C-rate, then flags whether your draw stays inside the safe continuous C-rate for LiPo, Li-ion, LiFePO4, NiMH, or lead-acid chemistry.

🎯Real Battery Pack Presets

🔋Battery and Load Inputs

Solve for

Choose the unknown; enter the matching values below.

Battery chemistry

Sets the safe max continuous C-rate for the verdict.

Battery capacity

Rated cell or pack capacity at the chosen unit.

Capacity unit

1000 mAh equals 1 Ah.

C-rate (C)

Multiple of capacity per hour, used when solving current or time.

Discharge current (A)

Actual load in amps, used when solving C-rate or time.

Runtime input basis

Only applies when solving for discharge time.

Usable depth of discharge (%)

Fraction of capacity actually drawn before cutoff.

Discharge Current 0 A I = C-rate x capacity

C-Rate 0 C C-rate = current / capacity

Discharge Time 0 h ideal runtime = 1 / C-rate

Safe Limit Verdict OK vs max continuous C-rate

🔢Formula Snapshot

IC-rate × Ah

Camps / Ah

t1 / C-rate

1000mAh per Ah

📋Capacity and C-Rate to Current

Capacity	C-Rate	Current I = C x Ah	Ideal Runtime
100 Ah	0.5C	50 A	2 h
100 Ah	1C	100 A	1 h
2.2 Ah	25C	55 A	2.4 min
1.5 Ah	30C	45 A	2 min
5.0 Ah	2C	10 A	30 min
50 Ah	0.2C	10 A	5 h
3.0 Ah	10C	30 A	6 min
200 Ah	0.05C	10 A	20 h

📊C-Rate to Runtime Reference

C-Rate	Ideal Runtime	In Minutes	Typical Use
0.05C	20 h	1200 min	Standby float
0.2C	5 h	300 min	Solar storage
0.5C	2 h	120 min	LFP cycling
1C	1 h	60 min	Rated capacity
2C	0.5 h	30 min	Power tools
10C	0.1 h	6 min	RC / e-bike
25C	0.04 h	2.4 min	Drone flight
50C	0.02 h	1.2 min	Racing burst

🗃Chemistry vs Safe Continuous C-Rate Grid

Chemistry	Max Continuous C	Burst C (10-30s)	Typical Cycles	Nominal Volts/Cell	Best For
LiPo	10-30C	50-100C	150-300	3.7 V	Drones, RC
Li-ion (18650)	1-5C	7-10C	300-800	3.6 V	Packs, e-bike
LiFePO4	1-3C	5-10C	2000-6000	3.2 V	Solar, RV, EV
NiMH	0.5-2C	5-10C	500-1000	1.2 V	AA, hybrids
Lead-acid AGM	0.2-0.3C	1-3C	200-500	2.0 V	Cars, UPS
Lead-acid flooded	0.1-0.2C	0.5-1C	300-1200	2.0 V	Deep cycle

📏Capacity and Current Unit Conversions

Unit	Equals	In Base Unit	Note
1 Ah	1000 mAh	1 Ah	Amp-hour capacity
1 mAh	0.001 Ah	0.001 Ah	Milliamp-hour
1 A	1000 mA	1 A	Amp of current
1 C	1 x capacity/h	1 per hour	Full pack in one hour
1 h	60 min	3600 s	Runtime unit
0.5C	half capacity/h	2 h runtime	Common LFP rate

⚙Formula Breakdown

Current I = C-rate × AhDischarge current equals the C-rate multiplied by capacity in amp-hours. A 100 Ah pack at 0.5C draws I = 0.5 × 100 = 50 A.

C-rate = I / AhRearrange to rate a known load. Drawing 55 A from a 2.2 Ah LiPo is a C-rate of 55 / 2.2 = 25C.

Runtime t = 1 / C-rateIdeal hours before empty equals one over the C-rate. At 0.5C that is 1 / 0.5 = 2 hours; at 25C it is 1 / 25 h = 2.4 min.

Runtime t = Ah / IEquivalent form using amps. A 2.2 Ah pack at 55 A lasts 2.2 / 55 = 0.04 h, about 2.4 minutes ideal.

Usable time = t × DoDScale by usable depth of discharge. At 80% DoD a 2 hour ideal runtime becomes 2 × 0.8 = 1.6 hours.

Safe check: C-rate vs maxIf the requested C-rate exceeds the chemistry safe continuous limit, the pack overheats. Compare your C-rate to the grid above.

💡Discharge Safety Tips

Leave C-rate headroom: Sizing a load right at a pack rated max C runs it hot and shortens life. If a LiPo is rated 30C continuous, plan for about 20C, roughly 70% of the limit, so momentary spikes still stay inside spec. On a 2.2 Ah pack that means aiming near 44 A instead of the full 66 A.

Burst is not continuous: A 50C burst rating only holds for 10 to 30 seconds, not the whole run. A 1300 mAh pack rated 100C burst can hit 130 A for a launch, but its continuous 60C figure, about 78 A, is the number that governs sustained flight without overheating the cells.

When an e-bike’s range evaporates on cold mornings or a drone battery swells mid-flight, that’s typically not bad luck. That’s battery trouble; specifically, a mismatch between amount of power the battery chemistry can supply and the amount you’re trying to draw. That gap is expressed by the C-rate. A C-rate ties together time, capacity, and current into a single relationship.

You’ll find a calculator here that does the math for you. You will not have to guess whether your cells are being drained efficienty or damaged by a particular load.

What Is a C-Rate and Why It Matters for Your Battery

A C-rate is a multiple of the pack’s total capacity expressed per hour. It’s not an absolute number of electrons. For instance, if you have a 100Ah battery at a rate of 1C, it will discharge completely in one hour. That’s one hundred amps flowing for one hour. This means a hundred amp-hour bank are pushing one hundred amps. Half that amount over twice the time is 0.5C, meaning it flows half as many amps for twice as long.

So a big storage wall running at twenty-five C is nothing; a tiny little hobby cell at that same rate are an enormous draw. Convert the rate into real world amperage before connecting your load. Why? Because of scale effect. It’s driven by three equations. One: Current = C-rate * Capacity (in amp-hours). Two: C-rate = Current/Capacity. Three: Ideal run time = 1 / C-rate. Those three variables is tied together and with any two of them, you get the third.

Want to know what the rate calls for? Need to determine the rate the load requires? Want to know how long it lasts? We solve it for you from every angle. That way, there’s no need to remember which variable gets plugged into which spot in the equation.

To put this another way, consider distinction between storage and sport. Fifty amps for two hours from a one hundred amp-hour LiFePO4 bank is gentle on cycle life; that’s a half-C rate. But fifty-five amps for less than two minutes from a two-point-two amp-hour LiPo drone battery? That’s twenty-five C and empty fast. The math matches. The thermal load doesn’t. When cells is pushed harder then their internal resistance will permit, voltage drops and temperature also drops. But there’s a limit, and that’s because of the chemistry.

Racing LiPos handle from ten to thirty C continuously. They can bursts much higher for seconds. Cylindrical Li-ion generally top out at around five C. Lithium iron phosphate likes one to three C but will repay your patience in thousands of cycles. Lead-acid is most fragile. It wants to stay below 0.3C or it degrades quickly. You can see that clearly on the page reference table. That way you don’t guess, you match the application to the right material.

That’s where the confusion arises regarding burst ratings. On their labels, manufacturers lists continuous limits along with peak values, which are typically very short-lived bursts. While a hundred C sounds great, it’s only going to be sustainable for 10 to 30 seconds. If they runs longer, the cells will overheat. And it doesn’t matter what’s printed on the box. That’s why the calculator automatically flags this distinction. It alerts you if your draw can sustains only momentary spikes compared to extended drains.

The other thing that alters reality is depth of discharge. If you deplete the entire capacity, then your run time will be perfect. Realistically, though, you kill lead acid by going below 50% and you could of leave lithium packs down to 20% before they suffer premature death. Making the prediction in terms of usable depth keeps things honest. You don’t find yourself stranded with a seemingly full pack that’s not strong enough to get you around the last leg.

The solar panel and drone load examples are all presets so you can see how various loads will behave. It also demonstrates importance of leaving a thirty percent margin below the rated maximum to keep the packs cool and reliable. Sizing right respects both capacity and chemistry. Treating the C-rate as a speed limit instead of a suggestion is what gives you flat batteries. Get the rate right and then hit start and you’ll have more time with power on.