Grains: Archery Calculator1.2 - App Store

Build a better hunting arrow. Grains calculates your total arrow weight, FOC, arrow speed, kinetic energy and momentum in one simple archery calculator.

Four calculators, no account, no ads, nothing to buy. Numbers carry from one tab to the next, so you enter your arrow build once.

ARROW WEIGHT
When you build an arrow, you're working with many small components of different weights. Enter your shaft length and grains per inch (GPI), point or broadhead, insert, nock, vanes or fletching, wrap and any additional weight, and Grains adds up your total arrow weight in grains. Change one component and see right away how it affects the whole build.

FOC (FRONT OF CENTER)
Front of center is an important factor in building an accurate hunting arrow. Enter your arrow length and balance point to get your FOC percentage. Grains also explains how to get an accurate measurement and what an ideal setup looks like (most hunters aim for 10% to 15%).

ARROW SPEED
A slow arrow gives game more time to "jump the string." Enter your bow's IBO speed, draw length, draw weight and any weight on the string, and Grains estimates your arrow speed in fps using the standard IBO rules. It also shows your grains per pound and warns you when your arrow drops below 5, the minimum most bow makers require to keep your warranty.

KINETIC ENERGY AND MOMENTUM
A fast arrow with good FOC is only good if it carries enough energy. Grains calculates kinetic energy in ft-lbs from your arrow weight and speed, shows the game your setup is suited for, from small game to deer, elk and black bear to moose and grizzly, and shows momentum, the number many bowhunters use to judge penetration.

METRIC OR IMPERIAL
Results follow your region's units, or pick your own in Settings: speed in m/s, energy in joules, momentum in kg.m/s and total weight in grams alongside grains. Inputs stay in grains, inches and pounds, just like your spec sheets.

QUICK TO USE
Jump between fields with the arrows at the top of the screen, tap any label to edit it, and swipe down to put the keypad away.

Speed is an estimate based on IBO specs. For an exact number, chronograph your bow.

Version History Know when your arrow is too light for your bow. Speed now shows grains per pound, and warns you when you drop below 5, the minimum most bow makers require to keep your warranty.

See your arrow's momentum right next to its kinetic energy, the number many hunters use to judge penetration.

Results now follow your region's units, or pick your own in Settings: speed in m/s, energy in joules, momentum in kg·m/s and total weight in grams alongside grains. Inputs stay in grains, inches and pounds, just like your spec sheets.

Entering a setup is quicker. Jump between fields with the arrows at the top of the screen, tap any label to edit it, and swipe down to put the keypad away.

Plus some smaller fixes and improvements. 1.2 2d ago Bug fixes and improvements. 1.1 09/06/2023 1.0 06/27/2021