Backpack Sprayer Mix Calculator: 1, 2 & 4 Gallons

Enter the rate from your label

Backpack sprayer mix calculator

Product to add: 6 fl oz
Water to add: 3.95 gal
Percent solution: 1.17%
Covers

How it was calculated1.5 fl oz/gal × 4 gal = 6 fl oz1.5 ÷ 128 × 100 = 1.17%4 gal − 6 fl oz ÷ 128 = 3.95 gal

Showing the worked example. Turn on JavaScript to calculate your own numbers.

Same arithmetic as the app: Mix Ratio multiplies the label rate by the volume you mix and shows the percent solution; Tank Mix divides that volume by your application rate to get the area it covers, then multiplies by the rate. The app shows the product in fl oz or mL only (no teaspoons or tablespoons) and reminds you to add it to a partly filled tank, then top off; the water figure here is the volume you mix minus the product's own volume.

Labels for backpack and handheld sprayers state the dose one of two ways. Spot spraying usually gives an amount of concentrate per gallon of water, often with the equivalent percent solution. Lawns and broadcast work give an amount per 1,000 sq ft or per acre instead. Pick the type first — the two are easy to mix up when rushing — because a per-area rate also needs the spray volume your sprayer actually puts on that area before anyone can say how much goes in the tank.

The rate itself comes from your label, for your product and target. SprayMaster ships no product rates and makes no recommendations; every example on this page uses a made-up label rate so you can follow the arithmetic.

4-gallon sprayer calculation

With a per-gallon label, product to add = rate × gallons mixed. The water is what is left after the concentrate's own volume (128 fl oz in a gallon), which is why a 4 gal mix at 1.5 fl oz per gallon reads 3.95 gal of water rather than 4.

Per-gallon label, hypothetical rate of 1.5 fl oz per gallon
Tank	Product to Add	Water	Percent Solution
1 gal	1.5 fl oz	0.988 gal	1.17%
2 gal	3 fl oz	1.98 gal	1.17%
4 gal	6 fl oz	3.95 gal	1.17%

Open Mix Ratio from the Calculators section. It is free.
Set Units to US for fl oz and gallons, or Metric for mL and litres.
Under Dilution, type the Label Rate per gallon and leave the Product Unit on fl oz.
Type the gallons you will mix as Tank Size: 4 for a full 4 gal backpack.
Read Product to Add and the Percent Solution under Mix, then tap Save to keep it in History.

The percent solution is the concentrate's share of the finished spray: 1.5 fl oz ÷ 128 × 100 = 1.17%. It only appears for fl oz or mL, because a product in lb has no volume percent. If your label gives a percent instead of ounces, multiply it by 1.28 to get fl oz per gallon (2% = 2.56 fl oz per gallon); the Rate Converter in SprayMaster Pro does this under Conversion, but the multiplication is quick by hand.

Per-gallon versus per-area rates

A lawn label such as 1.5 fl oz per 1,000 sq ft says nothing about the tank until you know how much spray you put on 1,000 sq ft. Measure it: fill the sprayer with plain water, spray a marked 1,000 sq ft at your normal pace and note how much is gone. At 1 gallon per 1,000 sq ft, a 4 gal tank covers 4,000 sq ft and takes 1.5 × 4 = 6 fl oz. At 2 gallons per 1,000 sq ft, the same tank covers 2,000 sq ft and takes 3 fl oz: same product, half the dose per tank.

Typing that 1.5 as a per-gallon rate would give 6 fl oz for the 4 gal tank in both cases, twice the label dose at the slower pace. That is the mistake the type selector in the calculator above guards against.

Per-area label, hypothetical rate of 1.5 fl oz per 1,000 sq ft, 4 gal tank
Spray volume	Covers	Product to Add	Water
1 gal per 1,000 sq ft	4 × 1,000 sq ft	6 fl oz	3.95 gal
2 gal per 1,000 sq ft	2 × 1,000 sq ft	3 fl oz	3.98 gal

In the app this is Tank Mix, not Mix Ratio. Set Rate Basis to Per 1,000 ft², type the Label Rate, the Tank Size and the Application Rate in GPA: 1 gallon per 1,000 sq ft is 43.56 GPA, because an acre is 43.56 thousand square feet. With 4 gal you get Product per Tank 6 fl oz and Covers per Tank 0.0918 acre. A per-acre label works the same with Per Acre and your GPA: 32 fl oz per acre at 20 GPA covers 0.2 acre per 4 gal tank and takes 6.4 fl oz.

Partial tank fills

You rarely need a full tank. Enter the volume you actually prepare, not the tank's capacity: at 1.5 fl oz per gallon, 2.5 gal in a 4 gal backpack takes 3.75 fl oz of product and 2.47 gal of water. In Mix Ratio that means typing 2.5 as Tank Size; the field is the batch size, and nothing in the app assumes a full tank.

Add the product to a partly filled tank, then top off with water: that is the app's own reminder under the result, and the mixing order on your label comes first.
Measure in the unit the answer shows, with a marked cup or syringe. Neither the calculator nor the app converts fl oz to teaspoons or tablespoons.
Mix only what you will spray that day, and label any sprayer that still holds mix.
Wear the protective equipment the label lists, even for a 1 gallon job.

Save calculations on your iPhone

Tap Save on any calculator and the result lands in History with date and time, so next weekend you reopen the 4 gal mix instead of working it out again. Mix Ratio, Tank Mix (per gallon, per 1,000 ft² and per acre), the US / metric switch and History are free, with a banner on the home list and a full-screen ad every third time you open Mix Ratio or Tank Mix. Everything runs on the phone, so it works at the back of the yard with no signal.

SprayMaster Pro adds Sprayer Calibration, the Rate Converter and Area / Acreage, and drops the ads. Calibrating a boom sprayer needs Pro. The per-1,000 sq ft measurement above doesn't, though — that one's just a bucket and a tape, and the app has no part in it.

In metric the same arithmetic runs in mL and litres: 20 mL per litre in a 15 L knapsack sprayer is 300 mL of product, 14.7 L of water and a 2% solution.

Questions and answers

How many ounces go in a 4 gallon backpack sprayer?

Four times the per-gallon rate on your label. SprayMaster has no product rates; it multiplies yours by the gallons you mix and shows the percent solution. At a hypothetical 1.5 fl oz per gallon that is 6 fl oz.

Is the backpack sprayer calculator the same math as the app?

Yes. The calculator on this page and the app's Mix Ratio and Tank Mix use the same formulas and rounding, checked against the app's code. The app adds Save and History and works offline.

My label says 2%: how many ounces per gallon is that?

Multiply the percent by 1.28. A 2% solution is 2.56 fl oz of concentrate per gallon of finished spray; the Rate Converter in SprayMaster Pro gives the same figure.

Is Mix Ratio free?

Yes. Mix Ratio, Tank Mix and History are free, with ads. Sprayer Calibration, the Rate Converter and Area / Acreage need SprayMaster Pro, which also removes the ads.

Can I use litres instead of gallons?

Yes. Switch the calculator or the app to metric and the rate is in mL per litre and the tank in litres, with the same percent solution.

How to convert a per-acre rate to per 1,000 sq ft, and back · SprayMaster

Calculate the mix for your backpack sprayer