How much do I need, and what will it cost me?
Small calculators for home and car questions. We work out the quantity from facts checked against two independent publishers; you type your own price, and the calculator multiplies it in your browser.
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Calculators
Walls, floors and rooms Building and outdoor projects Yard, garden and pool Energy and home systems Kitchen and parties Measure and convert Car, tools and tech
Walls, floors and rooms
- TileHow much tile do I need?Area, tile size and layout give the number of tiles with the right extra for cuts, the boxes, and the 50 lb bags of thin-set for your trowel notch. Figures from tile makers and mortar data sheets.
- PaintHow much paint do I need?Measure the room, take off doors and windows, pick one or two coats: the calculator gives gallons and quarts from makers' coverage figures, and the cost at the price you type.
- FlooringHow much flooring do I need?Room size plus the right extra for your floor: 10 percent for laminate and vinyl plank, 15 for a diagonal layout, 20 for carpet. Whole boxes from the square feet printed on yours, carpet in square yards.
- WallpaperHow many rolls of wallpaper do I need?Wall area minus doors and windows, divided by about 56 sq ft for a US double roll or 54 for a Euro roll, plus a spare roll. Why to buy one batch number, and what a pattern repeat costs.
- InsulationHow much insulation do I need?R-30 to R-60 for attics by climate zone, R-13 to R-21 for walls. Divide the R you need by the R per inch of batts, blown fiberglass, cellulose or spray foam to get the depth.
- CurtainsHow wide and long should my curtains be?Rod 3 to 5 in past the frame each side and about 6 in above it; curtains about 2 times the rod width (1.5 to 3); length from the rod to floating, kissing or puddling on the floor.
- DrywallHow much drywall do I need?Walls plus ceiling, divided by 32 or 48 sq ft a sheet, plus about 10 percent: the sheets. Then about 350 to 370 ft of tape and 120 to 140 lb of compound per 1,000 sq ft, from the makers.
- Rug sizeWhat size rug do I need?Leave 18 to 24 in of bare floor at the walls, get the front legs of the furniture on the rug, 24 in past the dining table, 18 to 24 in past the bed: 8x10 for most living rooms and queen beds, 9x12 for king.
Building and outdoor projects
- DeckHow many deck boards do I need?Deck size and board length give the boards to order with 10 percent extra, the joists at 16 or 12 in on center, and the screws or hidden clips. Board sizes and spacing from decking makers.
- FenceHow much fencing do I need?Type each straight run of your fence: the calculator counts posts at 6 or 8 ft, rails for the height, pickets by their real width, and 50 lb bags of concrete for holes a third of the post deep.
- StairsHow do I calculate stairs?Divide the total rise by about 7 inches to get the risers, then the exact riser height, the treads, the run and the stringer. With the IRC limits: risers at most 7 3/4 in, treads at least 10 in.
- ConcreteHow much concrete do I need?Length, width and thickness give cubic feet; makers' bag yields turn them into 40, 60 or 80 lb bags, or cubic yards for a truck. Post holes too, with 10 percent extra.
- RoofingHow many shingles do I need?From the house footprint and the roof pitch, the calculator finds the roof area, the squares and the bundles with the right waste for your roof shape, plus starter strip and ridge caps.
- BricksHow many bricks do I need?Modular brick with 3/8 in joints: about 6.75 to 7 bricks per square foot of wall, and about 7 to 8 bags of masonry cement per 1,000 bricks. Net area and extra for breakage.
- Deck stainHow much stain do I need?Area times coats divided by the coverage on your can: semi-transparent deck stains list roughly 250 to 300 sq ft per gallon for a first coat. Fences both sides, rough wood, and the water test.
- SidingHow much siding do I need?Siding is ordered by the square, 100 sq ft. Measure every wall without taking off windows and doors, add the gables, then 10 percent for waste.
- Board feetHow do I calculate board feet?A board foot is 144 cubic inches; board feet = thickness x width (inches) x length (feet) / 12. Why a 2x4 counts as 2 by 4, and hardwood quarters (4/4, 8/4).
- RebarHow much rebar do I need?Count the bars and the total feet of rebar for a slab grid at the spacing on your plans, with bar sizes explained: #4 is 1/2 inch, #5 is 5/8. Spacing and laps come from the plans.
- Concrete blockHow many concrete blocks do I need?Standard 8 x 8 x 16 in blocks: 1.125 per square foot of wall face, and about 3 bags of mortar per 100 blocks. Why an 8 x 16 block measures 7-5/8 x 15-5/8.
- PlywoodHow many sheets of plywood do I need?Area divided by 32 sq ft per 4 x 8 sheet, plus about 10 percent. Why a 3/4 inch sheet measures 23/32, what a 24/16 span rating means, and the 1/8 inch gap.
Yard, garden and pool
- GravelHow much gravel do I need?Length x width x depth in feet / 27 gives cubic yards. Depths: 2 to 4 in for a path, at least 4 in for a driveway, in compacted layers. Pea gravel or crushed stone, and landscape fabric.
- Pool chlorineHow much chlorine does my pool need?Work out your pool's gallons, then the chlorine to go from your reading to 1 to 3 ppm: about 10 to 11 fl oz of 12.5 percent liquid, or 2 oz of cal-hypo, per ppm per 10,000 gallons. Safety rules included.
- FertilizerHow much fertilizer do I need?Pounds per 1,000 sq ft to apply 1 lb of nitrogen = 100 divided by the first number on the bag: 6.25 lb of 16-4-8. Never more than 1 lb of nitrogen at once, and the spreader setting on the bag.
- Mulch, soil, gravelHow much mulch, soil or gravel do I need?Area x depth / 324 gives cubic yards; the calculator also counts 2 or 3 cubic foot bags. Depths from university extension services for mulch, a new lawn and a gravel path.
- PaversHow many pavers do I need?Area divided by one paver's area gives the count; under it, 6 to 8 inches of compacted gravel and about 1 inch of bedding sand. Edge restraint and polymeric sand joints.
- SodHow much sod do I need?Lawn area plus 5 to 10 percent, divided by 10 sq ft per roll or about 2.67 per slab; a pallet covers about 400 to 500 sq ft, varying by farm. Lay it the day it arrives.
- Grass seedHow much grass seed do I need?Tall fescue about 6 lb per 1,000 sq ft, Kentucky bluegrass about 2, fine fescue 4 to 6, bermudagrass 1 to 2: extension seeding rates, and about half for overseeding.
- Pool saltHow much salt does my pool need?About 8.3 lb of salt per 1,000 gallons for each 1,000 ppm: 10,000 gallons from zero to 3,200 ppm take about 267 lb. Test first, add the difference, and how much to drain when it is too salty.
- Plants per square footHow many plants per square foot?In a square foot garden each 1 ft square takes 1, 4, 9 or 16 plants: one tomato, four lettuces, nine beets, sixteen carrots. Count a whole bed with the calculator.
- Lawn waterHow much water does my lawn need?About 1 inch a week, rain included (1 to 1.5 in guides): about 620 gallons per 1,000 sq ft. The tuna-can test turns it into sprinkler minutes; water deeply, early in the morning.
Energy and home systems
- Heating BTUHow many BTU do I need to heat my home?Square feet times 30 to 60 BTU, by climate, gives the heat a home needs; the furnace label's input BTU times its AFUE gives what it delivers. Why a contractor's Manual J is the real answer.
- EV chargingHow much does it cost to charge an electric car?Miles x the car's kWh per 100 miles gives the energy; your own rate per kWh gives the cost. A calculator with EPA figures for five popular cars, and Level 1 and Level 2 charging times.
- GeneratorWhat size generator do I need?Add the running watts of what runs together, then the largest starting surge: the makers' sizing rule, with chart figures for a refrigerator and a sump pump, and the safety rules that go with it.
- SolarHow many solar panels do I need?Your yearly kWh from your bills, what one kW makes where you live, and the watts of one panel: the calculator gives the system size, the number of panels and the roof area they take.
- Breaker and wireWhat size breaker and wire do I need?Turn watts into amps, apply the 80 percent rule for long-running loads, and match the breaker to its copper wire: 14 gauge for 15 A, 12 for 20 A, 10 for 30 A. For a licensed electrician to install.
- Water heaterWhat size water heater do I need?For a tank, add the hot water of your busiest hour and match the first hour rating; for tankless, add the flow of fixtures running together at your temperature rise. Figures from the energy.gov worksheet.
- Room ACWhat size air conditioner do I need?The ENERGY STAR chart turns a room's square feet into BTU per hour, then adjusts for sun, shade, people and kitchens. Bigger is not better: why an oversized unit leaves a room cold and damp.
- Home kWhHow much electricity does a house use?An average US home uses about 10,700 to 10,800 kWh a year, roughly 900 a month. Type your bill's kWh to see your daily use and where you stand; heating, cooling and hot water lead.
- Appliance kWhHow much electricity does my appliance use?Watts times hours a day divided by 1,000 gives kWh a day, and a year; the calculator multiplies by your own rate. Where to find the watts, why a fridge counts a third, and phantom power.
- DehumidifierWhat size dehumidifier do I need?About 20 pints a day for 400 sq ft of damp space and about 50 for 1,200 or more, on the 2020 ratings. Why an old 50-pint unit is a new 30-pint, and the 30 to 50 percent humidity target.
- Ceiling fanWhat size ceiling fan do I need?From 29 to 36 inch blades for a room up to 75 sq ft to 50 to 54 inches up to 400 sq ft; blades 7 ft above the floor, 18 in from walls, and which way to spin in summer and winter.
Kitchen and parties
- Ounces in a cupHow many ounces in a cup?A US cup is 8 fluid ounces, about 236.6 ml. Why a cup of flour does not weigh 8 ounces, how the metric and UK measures differ, and a converter for cups, ounces, spoons and milliliters.
- Tablespoons in a cupHow many tablespoons in a cup?16 tablespoons in a cup, 3 teaspoons in a tablespoon, 2 tablespoons in a fluid ounce. A converter and the common in-between amounts: 1/4 cup, 1/3 cup, a stick of butter.
- Grams in an ounceHow many grams in an ounce?One ounce is 28.35 grams (exactly 28.349523125); a pound is 453.6 grams. Why gold uses a heavier troy ounce, and why a fluid ounce has no fixed weight. With a converter.
- Cups in a poundHow many cups in a pound?A pound of granulated sugar is about 2 1/4 cups, all-purpose flour 3 1/3 to 4, powdered sugar 3 1/2 to 4, butter 2. A converter both ways, and why the answer changes with the ingredient.
- Rice and waterHow much water for rice?Long-grain white rice takes 1 1/2 to 2 cups of water per cup on the stove, brown rice 1 3/4 to 2 1/2. One cup of dry white rice makes about 3 cooked. Why a rice cooker cup is smaller.
- Coffee ratioWhat is the coffee to water ratio?1 to 2 tablespoons per 6 ounces of water (National Coffee Association), or 55 grams per liter (Specialty Coffee Association). Why a coffee maker cup is 5 ounces, and cold brew ratios.
- Party foodHow much food do I need for a party?About 12 appetizer pieces per person when they are the meal, 6 before a meal; 2 or 3 sides at 4 to 5 oz each; a slice of dessert each; pizzas counted at 8 slices. Children count as half.
- Meat per personHow much meat per person?1/2 lb of boneless meat per adult, 3/4 lb bone-in, a 1/3 lb burger each. A whole brisket cooks down to about half, so buy about 1 lb raw per person; pork shoulder about 2/3 lb. Safe temperatures included.
- Turkey per personHow much turkey per person?About 1 lb of whole turkey per adult, 1 1/2 for leftovers, half for children; 1/2 lb of boneless breast. With the refrigerator thawing days by weight and the 165 deg F rule.
- Pasta per personHow much pasta per person?One serving is 2 oz of dry pasta, about 1 cup cooked: 8 servings in a 1 lb box. Boil it in at least 4 to 6 quarts of water per pound, without oil.
- Ham per personHow much ham per person?About 1/2 lb of bone-in ham per person (3/4 for big appetites) or 1/3 lb boneless; a 5 lb bone-in ham serves 8 to 10. Leftovers and reheating temperatures included.
- Ice for a partyHow much ice do I need for a party?Plan 1 to 2 lb of ice per guest for drinks, double it outdoors or on a hot day, and twice as much ice as contents in a cooler. The calculator counts the 10 lb bags.
- Drinks for a partyHow much alcohol do I need for a party?Plan 2 drinks per guest in the first hour, then 1 an hour; a 750 ml bottle pours 5 glasses of wine or about 16 shots; a half-barrel keg holds about 165 beers. Split by your guests' tastes.
Measure and convert
- Feet in a mileHow many feet in a mile?A mile is 5,280 feet, 1,760 yards and 1,609.344 meters. Why four laps of a track fall short of a mile, and roughly how many steps it takes, with a converter.
- Square feetHow do I calculate square footage?Add up to four shapes for any room, yard or garden bed, in square feet, square yards and square meters. And what counts in a home's official square footage under the ANSI standard.
- GallonsHow many gallons does it hold?Inches multiplied and divided by 231 give a tank's US gallons; pools in feet use 7.5 for rectangles and 5.9 for round and oval. Liters and imperial gallons too.
- Cubic feetHow do I calculate cubic feet?Length times width times height gives cubic feet; inches divide by 1,728; cubic yards are cubic feet / 27; a cylinder is 3.14 x radius squared x height. With gallons.
Car, tools and tech
- TowingHow much can I tow?Your tow rating is in the manual or on the door label; the whole loaded trailer must stay under it. Tongue weight runs about 10 to 15 percent of the trailer and counts against your payload.
- StorageHow much storage do I need?256 GB covers email, browsing, office and streaming; a gaming PC wants 512 GB to 1 TB, since big games take 100 GB each. 4K phone video takes about 24 GB an hour.
- RAMHow much RAM do I need?Windows 11 needs 4 GB but 8 GB is the practical floor; 16 GB for everyday multitasking; 16 to 32 GB for gaming; 32 GB to start for video editing; 64 GB or more for heavy professional work.
- Power supplyWhat size power supply do I need?Add the processor, graphics card and the rest, then about 150 W of headroom (100 to 200), and never go under the card maker's minimum system power. 80 PLUS levels explained.
- Gas for a tripHow much gas will my trip use?Gallons = miles / MPG; tick round trip and type your price per gallon. Why fast highway driving uses more than the rating, and how to measure your own MPG at the pump.
- Internet speedHow much internet speed do I need?About 25 Mbps per person, or add it up: 15 to 20 Mbps per 4K stream, about 5 for 1080p, 1.5 to 4 up and down per video call. The FCC benchmark is 100/20.
- Air compressorWhat size air compressor do I need?Read each tool's CFM at 90 PSI, size the compressor for the hungriest one, and buy above it, not equal. Why CFM beats tank size and horsepower, and when a bigger tank matters.
- TV sizeWhat size TV should I get?Screen size times about 1.2 gives a close seating distance: from 8 ft, up to about an 80 in screen. SMPTE's 30 degree and THX's 36 degree viewing angles, and why 4K lets you sit closer.
- Storage unitWhat size storage unit do I need?A 5x10 holds about one room, a 10x15 a two-bedroom home, a 10x20 a house with several bedrooms; units are about 8 ft tall, so a 10x10 holds about 800 cubic feet.
More calculators are being checked, one fact at a time, before they go up.
Why we never write a price
A price on a web page is out of date the week it is published, and it is rarely the price in your store, your town or your utility plan. So we split every question in two. The quantity part does not change from store to store: how many kWh for 100 miles, how many gallons for a room. We check it against two publishers and give the source. The money part is yours: type the price from your bill or your store, and the calculator does the multiplication on your device. Nothing you type is sent to us.
How we work
Every fact rests on two independent publishers and is numbered to its sources. Read how we check.