Short answer: a free-float handguard has to reach past the gas block. That means at least about 7 inches for carbine gas, 9 inches for mid-length and 12 inches for rifle gas, with a low-profile gas block underneath. Most builders go longer, stopping an inch or two short of the muzzle so the muzzle device still fits: on a 16-inch barrel that's usually a 13 to 15-inch handguard.
Handguard length by gas system
| Gas system | Gas block at about | Shortest free-float | Common choices |
|---|---|---|---|
| Carbine | 7 in | About 7 in | 9 to 15 in on a 16-inch barrel |
| Mid-length | 9 in | About 9 in | 10 to 15 in on a 16-inch barrel |
| Rifle | 12 in | About 12 in | 13 to 17 in on a 20-inch barrel |
Drop-in or free-float?
A drop-in handguard matches the gas system length exactly (carbine or mid-length), keeps the standard barrel nut and stops at the front sight base. A free-float handguard uses its own barrel nut, needs a low-profile gas block if it covers the block, and can be any length that clears the block and the muzzle device.
Not sure of your gas system? See the gas system length chart, and check the gas block fits under the handguard with our gas block size guide.
Parts that fit
Compare AR-15 handguards by length, attachment and price. The AR-15 builder warns when a handguard is too short for your barrel's gas system.
Frequently asked questions
What length handguard for a mid-length gas system?
At least about 9 inches for a free-float handguard over a low-profile gas block; 12 to 15 inches is common on a 16-inch barrel.
What handguard length for a 16-inch barrel?
Usually 13 to 15 inches: long enough for a good grip and accessories, short enough for the muzzle device.
Can a handguard be shorter than the gas system?
Yes, if it ends behind the gas block or front sight base, like a drop-in handguard. A free-float handguard that covers the block needs a low-profile block.
How much room should I leave for the muzzle device?
Typically an inch or two between the end of the handguard and the muzzle, depending on the device.
