DIY Vape Tools
Coil Building Calculator: Wraps, Ohms and Battery Safety
Building your own coils for an RDA, RTA or RDTA gives you full control of the vape, but it only works if the numbers are right. This calculator does both jobs: set your wire, gauge, inner diameter and wraps to get the exact build resistance, or set a target resistance and get the wraps you need. It also shows the power at a full battery and checks the amp draw against your cell, so you build safely. Full guide below.
Read first. Rebuildables and mechanical (unregulated) mods are for experienced vapers who understand battery safety. A build that draws more current than your battery can safely deliver is dangerous. This tool is a guide, not a substitute for knowing your gear. If you are not confident, use a regulated mod, which manages current for you, or ready-made coils.
Coil calculator
Kanthal A1 round wire is the usual starting point. Change the wire, gauge, inner diameter and wraps and the results update instantly.
Wire
Build
Wraps
Estimate using standard wire resistivity (Kanthal A1 1.45, Ni80 1.09, SS316L 0.75 ohm mm²/m) and standard AWG diameters. Real wire and builds vary. Power shown is Ohm's law at a full 4.2V cell. Always check your battery datasheet and never exceed its continuous discharge rating.
Check a coil we sell
Would rather buy a ready-made coil than wind your own? Pick one of our premade coils below and see its resistance, the power it runs at and whether it is safe on your battery, then jump straight to the product.
Resistances are read from the product options. Where a coil is sold as a range, the safety check uses the lower resistance (worst case for amp draw). Dual assumes two identical coils wired in parallel. The wattage shown is a general starting guide for regulated mods; always follow the range printed on the coil and start low. Confirm the resistance on your own device with an ohm reader before firing.
How the calculator works
Coil resistance comes down to three things: the wire material, how thick the wire is, and how much of it you use. A longer, thinner run of higher-resistance wire gives more ohms; a shorter, thicker run of lower-resistance wire gives fewer. The maths is standard physics - resistance equals resistivity times length divided by cross-sectional area - and the wrap length is the number of wraps times the circumference of the coil, plus your legs. Dual coils sit in parallel, which halves the resistance for the same wraps.
Wire types, in plain terms
High resistance, easy to build, holds its shape well. Wattage mode only. The best wire to learn on.
Lower resistance than Kanthal, so it heats quicker for a more responsive vape. Wattage mode only.
Low resistivity, can be used in wattage or temperature control mode. A popular all-round stainless option.
Shop coil wire, cotton and ready-made premade coils if you would rather not wind your own.
Single vs dual, and MTL vs DTL builds
Single coils are simpler, sip less battery and suit mouth-to-lung (MTL) vaping. Dual coils halve the resistance and ramp harder, which suits direct-to-lung (DTL) cloud building but demands more from your battery. As a rough guide only, MTL builds usually sit above about 0.8 ohms, restricted DTL around 0.4 to 0.8 ohms, and airy sub-ohm DTL below about 0.4 ohms. These are conventions, not rules, and your device and airflow matter just as much.
Higher resistance single coils, lower power, more discreet. Best on MTL RTAs.
Mid resistance, more air and vapour without full cloud chasing.
Battery safety, the part that matters
Every battery has a continuous discharge rating (CDR), the maximum current in amps it can deliver safely without overheating. Your build must draw less than that, with a margin to spare. The calculator works out the worst-case draw at a full 4.2V cell using Ohm's law (amps equal volts divided by resistance) and flags it if it goes over the CDR you enter. Always use the manufacturer's CDR, never the higher “pulse” figure, which is not a reliable standard. On a regulated mod the board manages this, but on a mechanical mod there is no protection, so the numbers are on you.
Golden rules. Use matched batteries from a reputable brand; check wraps for shorts with an ohm reader before firing; never fire a build below your battery's safe amp limit; carry spare cells in a case, never loose in a pocket.
Coil building FAQs
Coil maths uses standard physics and established wire resistivity values (as used by reference tools such as Steam Engine) and standard AWG wire diameters. Battery safety guidance follows the widely accepted rule of building within a cell's continuous discharge rating. This page is general information, not a safety certification; always follow your battery and device manufacturer's instructions.